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1 | ------------------------------------------------------------------------------ |
| 2 | T H E /proc F I L E S Y S T E M | |
| 3 | ------------------------------------------------------------------------------ | |
| 4 | /proc/sys Terrehon Bowden <terrehon@pacbell.net> October 7 1999 | |
| 5 | Bodo Bauer <bb@ricochet.net> | |
| 6 | ||
| 7 | 2.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000 | |
| 8 | ------------------------------------------------------------------------------ | |
| 9 | Version 1.3 Kernel version 2.2.12 | |
| 10 | Kernel version 2.4.0-test11-pre4 | |
| 11 | ------------------------------------------------------------------------------ | |
| 12 | ||
| 13 | Table of Contents | |
| 14 | ----------------- | |
| 15 | ||
| 16 | 0 Preface | |
| 17 | 0.1 Introduction/Credits | |
| 18 | 0.2 Legal Stuff | |
| 19 | ||
| 20 | 1 Collecting System Information | |
| 21 | 1.1 Process-Specific Subdirectories | |
| 22 | 1.2 Kernel data | |
| 23 | 1.3 IDE devices in /proc/ide | |
| 24 | 1.4 Networking info in /proc/net | |
| 25 | 1.5 SCSI info | |
| 26 | 1.6 Parallel port info in /proc/parport | |
| 27 | 1.7 TTY info in /proc/tty | |
| 28 | 1.8 Miscellaneous kernel statistics in /proc/stat | |
| 29 | ||
| 30 | 2 Modifying System Parameters | |
| 31 | 2.1 /proc/sys/fs - File system data | |
| 32 | 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats | |
| 33 | 2.3 /proc/sys/kernel - general kernel parameters | |
| 34 | 2.4 /proc/sys/vm - The virtual memory subsystem | |
| 35 | 2.5 /proc/sys/dev - Device specific parameters | |
| 36 | 2.6 /proc/sys/sunrpc - Remote procedure calls | |
| 37 | 2.7 /proc/sys/net - Networking stuff | |
| 38 | 2.8 /proc/sys/net/ipv4 - IPV4 settings | |
| 39 | 2.9 Appletalk | |
| 40 | 2.10 IPX | |
| 41 | 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem | |
| d7ff0dbf JFM |
42 | 2.12 /proc/<pid>/oom_adj - Adjust the oom-killer score |
| 43 | 2.13 /proc/<pid>/oom_score - Display current oom-killer score | |
| f9c99463 | 44 | 2.14 /proc/<pid>/io - Display the IO accounting fields |
| bb90110d | 45 | 2.15 /proc/<pid>/coredump_filter - Core dump filtering settings |
| 1da177e4 LT |
46 | |
| 47 | ------------------------------------------------------------------------------ | |
| 48 | Preface | |
| 49 | ------------------------------------------------------------------------------ | |
| 50 | ||
| 51 | 0.1 Introduction/Credits | |
| 52 | ------------------------ | |
| 53 | ||
| 54 | This documentation is part of a soon (or so we hope) to be released book on | |
| 55 | the SuSE Linux distribution. As there is no complete documentation for the | |
| 56 | /proc file system and we've used many freely available sources to write these | |
| 57 | chapters, it seems only fair to give the work back to the Linux community. | |
| 58 | This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm | |
| 59 | afraid it's still far from complete, but we hope it will be useful. As far as | |
| 60 | we know, it is the first 'all-in-one' document about the /proc file system. It | |
| 61 | is focused on the Intel x86 hardware, so if you are looking for PPC, ARM, | |
| 62 | SPARC, AXP, etc., features, you probably won't find what you are looking for. | |
| 63 | It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But | |
| 64 | additions and patches are welcome and will be added to this document if you | |
| 65 | mail them to Bodo. | |
| 66 | ||
| 67 | We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of | |
| 68 | other people for help compiling this documentation. We'd also like to extend a | |
| 69 | special thank you to Andi Kleen for documentation, which we relied on heavily | |
| 70 | to create this document, as well as the additional information he provided. | |
| 71 | Thanks to everybody else who contributed source or docs to the Linux kernel | |
| 72 | and helped create a great piece of software... :) | |
| 73 | ||
| 74 | If you have any comments, corrections or additions, please don't hesitate to | |
| 75 | contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this | |
| 76 | document. | |
| 77 | ||
| 78 | The latest version of this document is available online at | |
| 79 | http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version. | |
| 80 | ||
| 81 | If the above direction does not works for you, ypu could try the kernel | |
| 82 | mailing list at linux-kernel@vger.kernel.org and/or try to reach me at | |
| 83 | comandante@zaralinux.com. | |
| 84 | ||
| 85 | 0.2 Legal Stuff | |
| 86 | --------------- | |
| 87 | ||
| 88 | We don't guarantee the correctness of this document, and if you come to us | |
| 89 | complaining about how you screwed up your system because of incorrect | |
| 90 | documentation, we won't feel responsible... | |
| 91 | ||
| 92 | ------------------------------------------------------------------------------ | |
| 93 | CHAPTER 1: COLLECTING SYSTEM INFORMATION | |
| 94 | ------------------------------------------------------------------------------ | |
| 95 | ||
| 96 | ------------------------------------------------------------------------------ | |
| 97 | In This Chapter | |
| 98 | ------------------------------------------------------------------------------ | |
| 99 | * Investigating the properties of the pseudo file system /proc and its | |
| 100 | ability to provide information on the running Linux system | |
| 101 | * Examining /proc's structure | |
| 102 | * Uncovering various information about the kernel and the processes running | |
| 103 | on the system | |
| 104 | ------------------------------------------------------------------------------ | |
| 105 | ||
| 106 | ||
| 107 | The proc file system acts as an interface to internal data structures in the | |
| 108 | kernel. It can be used to obtain information about the system and to change | |
| 109 | certain kernel parameters at runtime (sysctl). | |
| 110 | ||
| 111 | First, we'll take a look at the read-only parts of /proc. In Chapter 2, we | |
| 112 | show you how you can use /proc/sys to change settings. | |
| 113 | ||
| 114 | 1.1 Process-Specific Subdirectories | |
| 115 | ----------------------------------- | |
| 116 | ||
| 117 | The directory /proc contains (among other things) one subdirectory for each | |
| 118 | process running on the system, which is named after the process ID (PID). | |
| 119 | ||
| 120 | The link self points to the process reading the file system. Each process | |
| 121 | subdirectory has the entries listed in Table 1-1. | |
| 122 | ||
| 123 | ||
| 124 | Table 1-1: Process specific entries in /proc | |
| 125 | .............................................................................. | |
| b813e931 DR |
126 | File Content |
| 127 | clear_refs Clears page referenced bits shown in smaps output | |
| 128 | cmdline Command line arguments | |
| 129 | cpu Current and last cpu in which it was executed (2.4)(smp) | |
| 130 | cwd Link to the current working directory | |
| 131 | environ Values of environment variables | |
| 132 | exe Link to the executable of this process | |
| 133 | fd Directory, which contains all file descriptors | |
| 134 | maps Memory maps to executables and library files (2.4) | |
| 135 | mem Memory held by this process | |
| 136 | root Link to the root directory of this process | |
| 137 | stat Process status | |
| 138 | statm Process memory status information | |
| 139 | status Process status in human readable form | |
| 140 | wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan | |
| 141 | smaps Extension based on maps, the rss size for each mapped file | |
| 1da177e4 LT |
142 | .............................................................................. |
| 143 | ||
| 144 | For example, to get the status information of a process, all you have to do is | |
| 145 | read the file /proc/PID/status: | |
| 146 | ||
| 147 | >cat /proc/self/status | |
| 148 | Name: cat | |
| 149 | State: R (running) | |
| 150 | Pid: 5452 | |
| 151 | PPid: 743 | |
| 152 | TracerPid: 0 (2.4) | |
| 153 | Uid: 501 501 501 501 | |
| 154 | Gid: 100 100 100 100 | |
| 155 | Groups: 100 14 16 | |
| 156 | VmSize: 1112 kB | |
| 157 | VmLck: 0 kB | |
| 158 | VmRSS: 348 kB | |
| 159 | VmData: 24 kB | |
| 160 | VmStk: 12 kB | |
| 161 | VmExe: 8 kB | |
| 162 | VmLib: 1044 kB | |
| 163 | SigPnd: 0000000000000000 | |
| 164 | SigBlk: 0000000000000000 | |
| 165 | SigIgn: 0000000000000000 | |
| 166 | SigCgt: 0000000000000000 | |
| 167 | CapInh: 00000000fffffeff | |
| 168 | CapPrm: 0000000000000000 | |
| 169 | CapEff: 0000000000000000 | |
| 170 | ||
| 171 | ||
| 172 | This shows you nearly the same information you would get if you viewed it with | |
| 173 | the ps command. In fact, ps uses the proc file system to obtain its | |
| 174 | information. The statm file contains more detailed information about the | |
| 18d96779 KC |
175 | process memory usage. Its seven fields are explained in Table 1-2. The stat |
| 176 | file contains details information about the process itself. Its fields are | |
| 177 | explained in Table 1-3. | |
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178 | |
| 179 | ||
| 180 | Table 1-2: Contents of the statm files (as of 2.6.8-rc3) | |
| 181 | .............................................................................. | |
| 182 | Field Content | |
| 183 | size total program size (pages) (same as VmSize in status) | |
| 184 | resident size of memory portions (pages) (same as VmRSS in status) | |
| 185 | shared number of pages that are shared (i.e. backed by a file) | |
| 186 | trs number of pages that are 'code' (not including libs; broken, | |
| 187 | includes data segment) | |
| 188 | lrs number of pages of library (always 0 on 2.6) | |
| 189 | drs number of pages of data/stack (including libs; broken, | |
| 190 | includes library text) | |
| 191 | dt number of dirty pages (always 0 on 2.6) | |
| 192 | .............................................................................. | |
| 193 | ||
| 18d96779 KC |
194 | |
| 195 | Table 1-3: Contents of the stat files (as of 2.6.22-rc3) | |
| 196 | .............................................................................. | |
| 197 | Field Content | |
| 198 | pid process id | |
| 199 | tcomm filename of the executable | |
| 200 | state state (R is running, S is sleeping, D is sleeping in an | |
| 201 | uninterruptible wait, Z is zombie, T is traced or stopped) | |
| 202 | ppid process id of the parent process | |
| 203 | pgrp pgrp of the process | |
| 204 | sid session id | |
| 205 | tty_nr tty the process uses | |
| 206 | tty_pgrp pgrp of the tty | |
| 207 | flags task flags | |
| 208 | min_flt number of minor faults | |
| 209 | cmin_flt number of minor faults with child's | |
| 210 | maj_flt number of major faults | |
| 211 | cmaj_flt number of major faults with child's | |
| 212 | utime user mode jiffies | |
| 213 | stime kernel mode jiffies | |
| 214 | cutime user mode jiffies with child's | |
| 215 | cstime kernel mode jiffies with child's | |
| 216 | priority priority level | |
| 217 | nice nice level | |
| 218 | num_threads number of threads | |
| 2e01e00e | 219 | it_real_value (obsolete, always 0) |
| 18d96779 KC |
220 | start_time time the process started after system boot |
| 221 | vsize virtual memory size | |
| 222 | rss resident set memory size | |
| 223 | rsslim current limit in bytes on the rss | |
| 224 | start_code address above which program text can run | |
| 225 | end_code address below which program text can run | |
| 226 | start_stack address of the start of the stack | |
| 227 | esp current value of ESP | |
| 228 | eip current value of EIP | |
| 229 | pending bitmap of pending signals (obsolete) | |
| 230 | blocked bitmap of blocked signals (obsolete) | |
| 231 | sigign bitmap of ignored signals (obsolete) | |
| 232 | sigcatch bitmap of catched signals (obsolete) | |
| 233 | wchan address where process went to sleep | |
| 234 | 0 (place holder) | |
| 235 | 0 (place holder) | |
| 236 | exit_signal signal to send to parent thread on exit | |
| 237 | task_cpu which CPU the task is scheduled on | |
| 238 | rt_priority realtime priority | |
| 239 | policy scheduling policy (man sched_setscheduler) | |
| 240 | blkio_ticks time spent waiting for block IO | |
| 241 | .............................................................................. | |
| 242 | ||
| 243 | ||
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244 | 1.2 Kernel data |
| 245 | --------------- | |
| 246 | ||
| 247 | Similar to the process entries, the kernel data files give information about | |
| 248 | the running kernel. The files used to obtain this information are contained in | |
| 18d96779 | 249 | /proc and are listed in Table 1-4. Not all of these will be present in your |
| 1da177e4 LT |
250 | system. It depends on the kernel configuration and the loaded modules, which |
| 251 | files are there, and which are missing. | |
| 252 | ||
| 18d96779 | 253 | Table 1-4: Kernel info in /proc |
| 1da177e4 LT |
254 | .............................................................................. |
| 255 | File Content | |
| 256 | apm Advanced power management info | |
| 257 | buddyinfo Kernel memory allocator information (see text) (2.5) | |
| 258 | bus Directory containing bus specific information | |
| 259 | cmdline Kernel command line | |
| 260 | cpuinfo Info about the CPU | |
| 261 | devices Available devices (block and character) | |
| 262 | dma Used DMS channels | |
| 263 | filesystems Supported filesystems | |
| 264 | driver Various drivers grouped here, currently rtc (2.4) | |
| 265 | execdomains Execdomains, related to security (2.4) | |
| 266 | fb Frame Buffer devices (2.4) | |
| 267 | fs File system parameters, currently nfs/exports (2.4) | |
| 268 | ide Directory containing info about the IDE subsystem | |
| 269 | interrupts Interrupt usage | |
| 270 | iomem Memory map (2.4) | |
| 271 | ioports I/O port usage | |
| 272 | irq Masks for irq to cpu affinity (2.4)(smp?) | |
| 273 | isapnp ISA PnP (Plug&Play) Info (2.4) | |
| 274 | kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4)) | |
| 275 | kmsg Kernel messages | |
| 276 | ksyms Kernel symbol table | |
| 277 | loadavg Load average of last 1, 5 & 15 minutes | |
| 278 | locks Kernel locks | |
| 279 | meminfo Memory info | |
| 280 | misc Miscellaneous | |
| 281 | modules List of loaded modules | |
| 282 | mounts Mounted filesystems | |
| 283 | net Networking info (see text) | |
| 284 | partitions Table of partitions known to the system | |
| 8b60756a | 285 | pci Deprecated info of PCI bus (new way -> /proc/bus/pci/, |
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286 | decoupled by lspci (2.4) |
| 287 | rtc Real time clock | |
| 288 | scsi SCSI info (see text) | |
| 289 | slabinfo Slab pool info | |
| 290 | stat Overall statistics | |
| 291 | swaps Swap space utilization | |
| 292 | sys See chapter 2 | |
| 293 | sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4) | |
| 294 | tty Info of tty drivers | |
| 295 | uptime System uptime | |
| 296 | version Kernel version | |
| 297 | video bttv info of video resources (2.4) | |
| 298 | .............................................................................. | |
| 299 | ||
| 300 | You can, for example, check which interrupts are currently in use and what | |
| 301 | they are used for by looking in the file /proc/interrupts: | |
| 302 | ||
| 303 | > cat /proc/interrupts | |
| 304 | CPU0 | |
| 305 | 0: 8728810 XT-PIC timer | |
| 306 | 1: 895 XT-PIC keyboard | |
| 307 | 2: 0 XT-PIC cascade | |
| 308 | 3: 531695 XT-PIC aha152x | |
| 309 | 4: 2014133 XT-PIC serial | |
| 310 | 5: 44401 XT-PIC pcnet_cs | |
| 311 | 8: 2 XT-PIC rtc | |
| 312 | 11: 8 XT-PIC i82365 | |
| 313 | 12: 182918 XT-PIC PS/2 Mouse | |
| 314 | 13: 1 XT-PIC fpu | |
| 315 | 14: 1232265 XT-PIC ide0 | |
| 316 | 15: 7 XT-PIC ide1 | |
| 317 | NMI: 0 | |
| 318 | ||
| 319 | In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the | |
| 320 | output of a SMP machine): | |
| 321 | ||
| 322 | > cat /proc/interrupts | |
| 323 | ||
| 324 | CPU0 CPU1 | |
| 325 | 0: 1243498 1214548 IO-APIC-edge timer | |
| 326 | 1: 8949 8958 IO-APIC-edge keyboard | |
| 327 | 2: 0 0 XT-PIC cascade | |
| 328 | 5: 11286 10161 IO-APIC-edge soundblaster | |
| 329 | 8: 1 0 IO-APIC-edge rtc | |
| 330 | 9: 27422 27407 IO-APIC-edge 3c503 | |
| 331 | 12: 113645 113873 IO-APIC-edge PS/2 Mouse | |
| 332 | 13: 0 0 XT-PIC fpu | |
| 333 | 14: 22491 24012 IO-APIC-edge ide0 | |
| 334 | 15: 2183 2415 IO-APIC-edge ide1 | |
| 335 | 17: 30564 30414 IO-APIC-level eth0 | |
| 336 | 18: 177 164 IO-APIC-level bttv | |
| 337 | NMI: 2457961 2457959 | |
| 338 | LOC: 2457882 2457881 | |
| 339 | ERR: 2155 | |
| 340 | ||
| 341 | NMI is incremented in this case because every timer interrupt generates a NMI | |
| 342 | (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups. | |
| 343 | ||
| 344 | LOC is the local interrupt counter of the internal APIC of every CPU. | |
| 345 | ||
| 346 | ERR is incremented in the case of errors in the IO-APIC bus (the bus that | |
| 347 | connects the CPUs in a SMP system. This means that an error has been detected, | |
| 348 | the IO-APIC automatically retry the transmission, so it should not be a big | |
| 349 | problem, but you should read the SMP-FAQ. | |
| 350 | ||
| 38e760a1 JK |
351 | In 2.6.2* /proc/interrupts was expanded again. This time the goal was for |
| 352 | /proc/interrupts to display every IRQ vector in use by the system, not | |
| 353 | just those considered 'most important'. The new vectors are: | |
| 354 | ||
| 355 | THR -- interrupt raised when a machine check threshold counter | |
| 356 | (typically counting ECC corrected errors of memory or cache) exceeds | |
| 357 | a configurable threshold. Only available on some systems. | |
| 358 | ||
| 359 | TRM -- a thermal event interrupt occurs when a temperature threshold | |
| 360 | has been exceeded for the CPU. This interrupt may also be generated | |
| 361 | when the temperature drops back to normal. | |
| 362 | ||
| 363 | SPU -- a spurious interrupt is some interrupt that was raised then lowered | |
| 364 | by some IO device before it could be fully processed by the APIC. Hence | |
| 365 | the APIC sees the interrupt but does not know what device it came from. | |
| 366 | For this case the APIC will generate the interrupt with a IRQ vector | |
| 367 | of 0xff. This might also be generated by chipset bugs. | |
| 368 | ||
| 369 | RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are | |
| 370 | sent from one CPU to another per the needs of the OS. Typically, | |
| 371 | their statistics are used by kernel developers and interested users to | |
| 372 | determine the occurance of interrupt of the given type. | |
| 373 | ||
| 374 | The above IRQ vectors are displayed only when relevent. For example, | |
| 375 | the threshold vector does not exist on x86_64 platforms. Others are | |
| 376 | suppressed when the system is a uniprocessor. As of this writing, only | |
| 377 | i386 and x86_64 platforms support the new IRQ vector displays. | |
| 378 | ||
| 379 | Of some interest is the introduction of the /proc/irq directory to 2.4. | |
| 1da177e4 LT |
380 | It could be used to set IRQ to CPU affinity, this means that you can "hook" an |
| 381 | IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the | |
| 382 | irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask | |
| 383 | ||
| 384 | For example | |
| 385 | > ls /proc/irq/ | |
| 386 | 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask | |
| 387 | 1 11 13 15 17 19 3 5 7 9 | |
| 388 | > ls /proc/irq/0/ | |
| 389 | smp_affinity | |
| 390 | ||
| 391 | The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ | |
| 392 | is the same by default: | |
| 393 | ||
| 394 | > cat /proc/irq/0/smp_affinity | |
| 395 | ffffffff | |
| 396 | ||
| c30fe7f7 | 397 | It's a bitmask, in which you can specify which CPUs can handle the IRQ, you can |
| 1da177e4 LT |
398 | set it by doing: |
| 399 | ||
| 400 | > echo 1 > /proc/irq/prof_cpu_mask | |
| 401 | ||
| 402 | This means that only the first CPU will handle the IRQ, but you can also echo 5 | |
| c30fe7f7 | 403 | which means that only the first and fourth CPU can handle the IRQ. |
| 1da177e4 LT |
404 | |
| 405 | The way IRQs are routed is handled by the IO-APIC, and it's Round Robin | |
| 406 | between all the CPUs which are allowed to handle it. As usual the kernel has | |
| 407 | more info than you and does a better job than you, so the defaults are the | |
| 408 | best choice for almost everyone. | |
| 409 | ||
| 410 | There are three more important subdirectories in /proc: net, scsi, and sys. | |
| 411 | The general rule is that the contents, or even the existence of these | |
| 412 | directories, depend on your kernel configuration. If SCSI is not enabled, the | |
| 413 | directory scsi may not exist. The same is true with the net, which is there | |
| 414 | only when networking support is present in the running kernel. | |
| 415 | ||
| 416 | The slabinfo file gives information about memory usage at the slab level. | |
| 417 | Linux uses slab pools for memory management above page level in version 2.2. | |
| 418 | Commonly used objects have their own slab pool (such as network buffers, | |
| 419 | directory cache, and so on). | |
| 420 | ||
| 421 | .............................................................................. | |
| 422 | ||
| 423 | > cat /proc/buddyinfo | |
| 424 | ||
| 425 | Node 0, zone DMA 0 4 5 4 4 3 ... | |
| 426 | Node 0, zone Normal 1 0 0 1 101 8 ... | |
| 427 | Node 0, zone HighMem 2 0 0 1 1 0 ... | |
| 428 | ||
| 429 | Memory fragmentation is a problem under some workloads, and buddyinfo is a | |
| 430 | useful tool for helping diagnose these problems. Buddyinfo will give you a | |
| 431 | clue as to how big an area you can safely allocate, or why a previous | |
| 432 | allocation failed. | |
| 433 | ||
| 434 | Each column represents the number of pages of a certain order which are | |
| 435 | available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in | |
| 436 | ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE | |
| 437 | available in ZONE_NORMAL, etc... | |
| 438 | ||
| 439 | .............................................................................. | |
| 440 | ||
| 441 | meminfo: | |
| 442 | ||
| 443 | Provides information about distribution and utilization of memory. This | |
| 444 | varies by architecture and compile options. The following is from a | |
| 445 | 16GB PIII, which has highmem enabled. You may not have all of these fields. | |
| 446 | ||
| 447 | > cat /proc/meminfo | |
| 448 | ||
| 449 | ||
| 450 | MemTotal: 16344972 kB | |
| 451 | MemFree: 13634064 kB | |
| 452 | Buffers: 3656 kB | |
| 453 | Cached: 1195708 kB | |
| 454 | SwapCached: 0 kB | |
| 455 | Active: 891636 kB | |
| 456 | Inactive: 1077224 kB | |
| 457 | HighTotal: 15597528 kB | |
| 458 | HighFree: 13629632 kB | |
| 459 | LowTotal: 747444 kB | |
| 460 | LowFree: 4432 kB | |
| 461 | SwapTotal: 0 kB | |
| 462 | SwapFree: 0 kB | |
| 463 | Dirty: 968 kB | |
| 464 | Writeback: 0 kB | |
| 465 | Mapped: 280372 kB | |
| 466 | Slab: 684068 kB | |
| 467 | CommitLimit: 7669796 kB | |
| 468 | Committed_AS: 100056 kB | |
| 469 | PageTables: 24448 kB | |
| 470 | VmallocTotal: 112216 kB | |
| 471 | VmallocUsed: 428 kB | |
| 472 | VmallocChunk: 111088 kB | |
| 473 | ||
| 474 | MemTotal: Total usable ram (i.e. physical ram minus a few reserved | |
| 475 | bits and the kernel binary code) | |
| 476 | MemFree: The sum of LowFree+HighFree | |
| 477 | Buffers: Relatively temporary storage for raw disk blocks | |
| 478 | shouldn't get tremendously large (20MB or so) | |
| 479 | Cached: in-memory cache for files read from the disk (the | |
| 480 | pagecache). Doesn't include SwapCached | |
| 481 | SwapCached: Memory that once was swapped out, is swapped back in but | |
| 482 | still also is in the swapfile (if memory is needed it | |
| 483 | doesn't need to be swapped out AGAIN because it is already | |
| 484 | in the swapfile. This saves I/O) | |
| 485 | Active: Memory that has been used more recently and usually not | |
| 486 | reclaimed unless absolutely necessary. | |
| 487 | Inactive: Memory which has been less recently used. It is more | |
| 488 | eligible to be reclaimed for other purposes | |
| 489 | HighTotal: | |
| 490 | HighFree: Highmem is all memory above ~860MB of physical memory | |
| 491 | Highmem areas are for use by userspace programs, or | |
| 492 | for the pagecache. The kernel must use tricks to access | |
| 493 | this memory, making it slower to access than lowmem. | |
| 494 | LowTotal: | |
| 495 | LowFree: Lowmem is memory which can be used for everything that | |
| 3f6dee9b | 496 | highmem can be used for, but it is also available for the |
| 1da177e4 LT |
497 | kernel's use for its own data structures. Among many |
| 498 | other things, it is where everything from the Slab is | |
| 499 | allocated. Bad things happen when you're out of lowmem. | |
| 500 | SwapTotal: total amount of swap space available | |
| 501 | SwapFree: Memory which has been evicted from RAM, and is temporarily | |
| 502 | on the disk | |
| 503 | Dirty: Memory which is waiting to get written back to the disk | |
| 504 | Writeback: Memory which is actively being written back to the disk | |
| 505 | Mapped: files which have been mmaped, such as libraries | |
| e82443c0 | 506 | Slab: in-kernel data structures cache |
| 1da177e4 LT |
507 | CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'), |
| 508 | this is the total amount of memory currently available to | |
| 509 | be allocated on the system. This limit is only adhered to | |
| 510 | if strict overcommit accounting is enabled (mode 2 in | |
| 511 | 'vm.overcommit_memory'). | |
| 512 | The CommitLimit is calculated with the following formula: | |
| 513 | CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap | |
| 514 | For example, on a system with 1G of physical RAM and 7G | |
| 515 | of swap with a `vm.overcommit_ratio` of 30 it would | |
| 516 | yield a CommitLimit of 7.3G. | |
| 517 | For more details, see the memory overcommit documentation | |
| 518 | in vm/overcommit-accounting. | |
| 519 | Committed_AS: The amount of memory presently allocated on the system. | |
| 520 | The committed memory is a sum of all of the memory which | |
| 521 | has been allocated by processes, even if it has not been | |
| 522 | "used" by them as of yet. A process which malloc()'s 1G | |
| 523 | of memory, but only touches 300M of it will only show up | |
| 524 | as using 300M of memory even if it has the address space | |
| 525 | allocated for the entire 1G. This 1G is memory which has | |
| 526 | been "committed" to by the VM and can be used at any time | |
| 527 | by the allocating application. With strict overcommit | |
| 528 | enabled on the system (mode 2 in 'vm.overcommit_memory'), | |
| 529 | allocations which would exceed the CommitLimit (detailed | |
| 530 | above) will not be permitted. This is useful if one needs | |
| 531 | to guarantee that processes will not fail due to lack of | |
| 532 | memory once that memory has been successfully allocated. | |
| 533 | PageTables: amount of memory dedicated to the lowest level of page | |
| 534 | tables. | |
| 535 | VmallocTotal: total size of vmalloc memory area | |
| 536 | VmallocUsed: amount of vmalloc area which is used | |
| 537 | VmallocChunk: largest contigious block of vmalloc area which is free | |
| 538 | ||
| 539 | ||
| 540 | 1.3 IDE devices in /proc/ide | |
| 541 | ---------------------------- | |
| 542 | ||
| 543 | The subdirectory /proc/ide contains information about all IDE devices of which | |
| 544 | the kernel is aware. There is one subdirectory for each IDE controller, the | |
| 545 | file drivers and a link for each IDE device, pointing to the device directory | |
| 546 | in the controller specific subtree. | |
| 547 | ||
| 548 | The file drivers contains general information about the drivers used for the | |
| 549 | IDE devices: | |
| 550 | ||
| 551 | > cat /proc/ide/drivers | |
| 552 | ide-cdrom version 4.53 | |
| 553 | ide-disk version 1.08 | |
| 554 | ||
| 555 | More detailed information can be found in the controller specific | |
| 556 | subdirectories. These are named ide0, ide1 and so on. Each of these | |
| 18d96779 | 557 | directories contains the files shown in table 1-5. |
| 1da177e4 LT |
558 | |
| 559 | ||
| 18d96779 | 560 | Table 1-5: IDE controller info in /proc/ide/ide? |
| 1da177e4 LT |
561 | .............................................................................. |
| 562 | File Content | |
| 563 | channel IDE channel (0 or 1) | |
| 564 | config Configuration (only for PCI/IDE bridge) | |
| 565 | mate Mate name | |
| 566 | model Type/Chipset of IDE controller | |
| 567 | .............................................................................. | |
| 568 | ||
| 569 | Each device connected to a controller has a separate subdirectory in the | |
| 18d96779 | 570 | controllers directory. The files listed in table 1-6 are contained in these |
| 1da177e4 LT |
571 | directories. |
| 572 | ||
| 573 | ||
| 18d96779 | 574 | Table 1-6: IDE device information |
| 1da177e4 LT |
575 | .............................................................................. |
| 576 | File Content | |
| 577 | cache The cache | |
| 578 | capacity Capacity of the medium (in 512Byte blocks) | |
| 579 | driver driver and version | |
| 580 | geometry physical and logical geometry | |
| 581 | identify device identify block | |
| 582 | media media type | |
| 583 | model device identifier | |
| 584 | settings device setup | |
| 585 | smart_thresholds IDE disk management thresholds | |
| 586 | smart_values IDE disk management values | |
| 587 | .............................................................................. | |
| 588 | ||
| 589 | The most interesting file is settings. This file contains a nice overview of | |
| 590 | the drive parameters: | |
| 591 | ||
| 592 | # cat /proc/ide/ide0/hda/settings | |
| 593 | name value min max mode | |
| 594 | ---- ----- --- --- ---- | |
| 595 | bios_cyl 526 0 65535 rw | |
| 596 | bios_head 255 0 255 rw | |
| 597 | bios_sect 63 0 63 rw | |
| 598 | breada_readahead 4 0 127 rw | |
| 599 | bswap 0 0 1 r | |
| 600 | file_readahead 72 0 2097151 rw | |
| 601 | io_32bit 0 0 3 rw | |
| 602 | keepsettings 0 0 1 rw | |
| 603 | max_kb_per_request 122 1 127 rw | |
| 604 | multcount 0 0 8 rw | |
| 605 | nice1 1 0 1 rw | |
| 606 | nowerr 0 0 1 rw | |
| 607 | pio_mode write-only 0 255 w | |
| 608 | slow 0 0 1 rw | |
| 609 | unmaskirq 0 0 1 rw | |
| 610 | using_dma 0 0 1 rw | |
| 611 | ||
| 612 | ||
| 613 | 1.4 Networking info in /proc/net | |
| 614 | -------------------------------- | |
| 615 | ||
| 616 | The subdirectory /proc/net follows the usual pattern. Table 1-6 shows the | |
| 617 | additional values you get for IP version 6 if you configure the kernel to | |
| 618 | support this. Table 1-7 lists the files and their meaning. | |
| 619 | ||
| 620 | ||
| 621 | Table 1-6: IPv6 info in /proc/net | |
| 622 | .............................................................................. | |
| 623 | File Content | |
| 624 | udp6 UDP sockets (IPv6) | |
| 625 | tcp6 TCP sockets (IPv6) | |
| 626 | raw6 Raw device statistics (IPv6) | |
| 627 | igmp6 IP multicast addresses, which this host joined (IPv6) | |
| 628 | if_inet6 List of IPv6 interface addresses | |
| 629 | ipv6_route Kernel routing table for IPv6 | |
| 630 | rt6_stats Global IPv6 routing tables statistics | |
| 631 | sockstat6 Socket statistics (IPv6) | |
| 632 | snmp6 Snmp data (IPv6) | |
| 633 | .............................................................................. | |
| 634 | ||
| 635 | ||
| 636 | Table 1-7: Network info in /proc/net | |
| 637 | .............................................................................. | |
| 638 | File Content | |
| 639 | arp Kernel ARP table | |
| 640 | dev network devices with statistics | |
| 641 | dev_mcast the Layer2 multicast groups a device is listening too | |
| 642 | (interface index, label, number of references, number of bound | |
| 643 | addresses). | |
| 644 | dev_stat network device status | |
| 645 | ip_fwchains Firewall chain linkage | |
| 646 | ip_fwnames Firewall chain names | |
| 647 | ip_masq Directory containing the masquerading tables | |
| 648 | ip_masquerade Major masquerading table | |
| 649 | netstat Network statistics | |
| 650 | raw raw device statistics | |
| 651 | route Kernel routing table | |
| 652 | rpc Directory containing rpc info | |
| 653 | rt_cache Routing cache | |
| 654 | snmp SNMP data | |
| 655 | sockstat Socket statistics | |
| 656 | tcp TCP sockets | |
| 657 | tr_rif Token ring RIF routing table | |
| 658 | udp UDP sockets | |
| 659 | unix UNIX domain sockets | |
| 660 | wireless Wireless interface data (Wavelan etc) | |
| 661 | igmp IP multicast addresses, which this host joined | |
| 662 | psched Global packet scheduler parameters. | |
| 663 | netlink List of PF_NETLINK sockets | |
| 664 | ip_mr_vifs List of multicast virtual interfaces | |
| 665 | ip_mr_cache List of multicast routing cache | |
| 666 | .............................................................................. | |
| 667 | ||
| 668 | You can use this information to see which network devices are available in | |
| 669 | your system and how much traffic was routed over those devices: | |
| 670 | ||
| 671 | > cat /proc/net/dev | |
| 672 | Inter-|Receive |[... | |
| 673 | face |bytes packets errs drop fifo frame compressed multicast|[... | |
| 674 | lo: 908188 5596 0 0 0 0 0 0 [... | |
| 675 | ppp0:15475140 20721 410 0 0 410 0 0 [... | |
| 676 | eth0: 614530 7085 0 0 0 0 0 1 [... | |
| 677 | ||
| 678 | ...] Transmit | |
| 679 | ...] bytes packets errs drop fifo colls carrier compressed | |
| 680 | ...] 908188 5596 0 0 0 0 0 0 | |
| 681 | ...] 1375103 17405 0 0 0 0 0 0 | |
| 682 | ...] 1703981 5535 0 0 0 3 0 0 | |
| 683 | ||
| 684 | In addition, each Channel Bond interface has it's own directory. For | |
| 685 | example, the bond0 device will have a directory called /proc/net/bond0/. | |
| 686 | It will contain information that is specific to that bond, such as the | |
| 687 | current slaves of the bond, the link status of the slaves, and how | |
| 688 | many times the slaves link has failed. | |
| 689 | ||
| 690 | 1.5 SCSI info | |
| 691 | ------------- | |
| 692 | ||
| 693 | If you have a SCSI host adapter in your system, you'll find a subdirectory | |
| 694 | named after the driver for this adapter in /proc/scsi. You'll also see a list | |
| 695 | of all recognized SCSI devices in /proc/scsi: | |
| 696 | ||
| 697 | >cat /proc/scsi/scsi | |
| 698 | Attached devices: | |
| 699 | Host: scsi0 Channel: 00 Id: 00 Lun: 00 | |
| 700 | Vendor: IBM Model: DGHS09U Rev: 03E0 | |
| 701 | Type: Direct-Access ANSI SCSI revision: 03 | |
| 702 | Host: scsi0 Channel: 00 Id: 06 Lun: 00 | |
| 703 | Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04 | |
| 704 | Type: CD-ROM ANSI SCSI revision: 02 | |
| 705 | ||
| 706 | ||
| 707 | The directory named after the driver has one file for each adapter found in | |
| 708 | the system. These files contain information about the controller, including | |
| 709 | the used IRQ and the IO address range. The amount of information shown is | |
| 710 | dependent on the adapter you use. The example shows the output for an Adaptec | |
| 711 | AHA-2940 SCSI adapter: | |
| 712 | ||
| 713 | > cat /proc/scsi/aic7xxx/0 | |
| 714 | ||
| 715 | Adaptec AIC7xxx driver version: 5.1.19/3.2.4 | |
| 716 | Compile Options: | |
| 717 | TCQ Enabled By Default : Disabled | |
| 718 | AIC7XXX_PROC_STATS : Disabled | |
| 719 | AIC7XXX_RESET_DELAY : 5 | |
| 720 | Adapter Configuration: | |
| 721 | SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter | |
| 722 | Ultra Wide Controller | |
| 723 | PCI MMAPed I/O Base: 0xeb001000 | |
| 724 | Adapter SEEPROM Config: SEEPROM found and used. | |
| 725 | Adaptec SCSI BIOS: Enabled | |
| 726 | IRQ: 10 | |
| 727 | SCBs: Active 0, Max Active 2, | |
| 728 | Allocated 15, HW 16, Page 255 | |
| 729 | Interrupts: 160328 | |
| 730 | BIOS Control Word: 0x18b6 | |
| 731 | Adapter Control Word: 0x005b | |
| 732 | Extended Translation: Enabled | |
| 733 | Disconnect Enable Flags: 0xffff | |
| 734 | Ultra Enable Flags: 0x0001 | |
| 735 | Tag Queue Enable Flags: 0x0000 | |
| 736 | Ordered Queue Tag Flags: 0x0000 | |
| 737 | Default Tag Queue Depth: 8 | |
| 738 | Tagged Queue By Device array for aic7xxx host instance 0: | |
| 739 | {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} | |
| 740 | Actual queue depth per device for aic7xxx host instance 0: | |
| 741 | {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} | |
| 742 | Statistics: | |
| 743 | (scsi0:0:0:0) | |
| 744 | Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 | |
| 745 | Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) | |
| 746 | Total transfers 160151 (74577 reads and 85574 writes) | |
| 747 | (scsi0:0:6:0) | |
| 748 | Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 | |
| 749 | Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) | |
| 750 | Total transfers 0 (0 reads and 0 writes) | |
| 751 | ||
| 752 | ||
| 753 | 1.6 Parallel port info in /proc/parport | |
| 754 | --------------------------------------- | |
| 755 | ||
| 756 | The directory /proc/parport contains information about the parallel ports of | |
| 757 | your system. It has one subdirectory for each port, named after the port | |
| 758 | number (0,1,2,...). | |
| 759 | ||
| 760 | These directories contain the four files shown in Table 1-8. | |
| 761 | ||
| 762 | ||
| 763 | Table 1-8: Files in /proc/parport | |
| 764 | .............................................................................. | |
| 765 | File Content | |
| 766 | autoprobe Any IEEE-1284 device ID information that has been acquired. | |
| 767 | devices list of the device drivers using that port. A + will appear by the | |
| 768 | name of the device currently using the port (it might not appear | |
| 769 | against any). | |
| 770 | hardware Parallel port's base address, IRQ line and DMA channel. | |
| 771 | irq IRQ that parport is using for that port. This is in a separate | |
| 772 | file to allow you to alter it by writing a new value in (IRQ | |
| 773 | number or none). | |
| 774 | .............................................................................. | |
| 775 | ||
| 776 | 1.7 TTY info in /proc/tty | |
| 777 | ------------------------- | |
| 778 | ||
| 779 | Information about the available and actually used tty's can be found in the | |
| 780 | directory /proc/tty.You'll find entries for drivers and line disciplines in | |
| 781 | this directory, as shown in Table 1-9. | |
| 782 | ||
| 783 | ||
| 784 | Table 1-9: Files in /proc/tty | |
| 785 | .............................................................................. | |
| 786 | File Content | |
| 787 | drivers list of drivers and their usage | |
| 788 | ldiscs registered line disciplines | |
| 789 | driver/serial usage statistic and status of single tty lines | |
| 790 | .............................................................................. | |
| 791 | ||
| 792 | To see which tty's are currently in use, you can simply look into the file | |
| 793 | /proc/tty/drivers: | |
| 794 | ||
| 795 | > cat /proc/tty/drivers | |
| 796 | pty_slave /dev/pts 136 0-255 pty:slave | |
| 797 | pty_master /dev/ptm 128 0-255 pty:master | |
| 798 | pty_slave /dev/ttyp 3 0-255 pty:slave | |
| 799 | pty_master /dev/pty 2 0-255 pty:master | |
| 800 | serial /dev/cua 5 64-67 serial:callout | |
| 801 | serial /dev/ttyS 4 64-67 serial | |
| 802 | /dev/tty0 /dev/tty0 4 0 system:vtmaster | |
| 803 | /dev/ptmx /dev/ptmx 5 2 system | |
| 804 | /dev/console /dev/console 5 1 system:console | |
| 805 | /dev/tty /dev/tty 5 0 system:/dev/tty | |
| 806 | unknown /dev/tty 4 1-63 console | |
| 807 | ||
| 808 | ||
| 809 | 1.8 Miscellaneous kernel statistics in /proc/stat | |
| 810 | ------------------------------------------------- | |
| 811 | ||
| 812 | Various pieces of information about kernel activity are available in the | |
| 813 | /proc/stat file. All of the numbers reported in this file are aggregates | |
| 814 | since the system first booted. For a quick look, simply cat the file: | |
| 815 | ||
| 816 | > cat /proc/stat | |
| b68f2c3a LC |
817 | cpu 2255 34 2290 22625563 6290 127 456 0 |
| 818 | cpu0 1132 34 1441 11311718 3675 127 438 0 | |
| 819 | cpu1 1123 0 849 11313845 2614 0 18 0 | |
| 1da177e4 LT |
820 | intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...] |
| 821 | ctxt 1990473 | |
| 822 | btime 1062191376 | |
| 823 | processes 2915 | |
| 824 | procs_running 1 | |
| 825 | procs_blocked 0 | |
| 826 | ||
| 827 | The very first "cpu" line aggregates the numbers in all of the other "cpuN" | |
| 828 | lines. These numbers identify the amount of time the CPU has spent performing | |
| 829 | different kinds of work. Time units are in USER_HZ (typically hundredths of a | |
| 830 | second). The meanings of the columns are as follows, from left to right: | |
| 831 | ||
| 832 | - user: normal processes executing in user mode | |
| 833 | - nice: niced processes executing in user mode | |
| 834 | - system: processes executing in kernel mode | |
| 835 | - idle: twiddling thumbs | |
| 836 | - iowait: waiting for I/O to complete | |
| 837 | - irq: servicing interrupts | |
| 838 | - softirq: servicing softirqs | |
| b68f2c3a | 839 | - steal: involuntary wait |
| 1da177e4 LT |
840 | |
| 841 | The "intr" line gives counts of interrupts serviced since boot time, for each | |
| 842 | of the possible system interrupts. The first column is the total of all | |
| 843 | interrupts serviced; each subsequent column is the total for that particular | |
| 844 | interrupt. | |
| 845 | ||
| 846 | The "ctxt" line gives the total number of context switches across all CPUs. | |
| 847 | ||
| 848 | The "btime" line gives the time at which the system booted, in seconds since | |
| 849 | the Unix epoch. | |
| 850 | ||
| 851 | The "processes" line gives the number of processes and threads created, which | |
| 852 | includes (but is not limited to) those created by calls to the fork() and | |
| 853 | clone() system calls. | |
| 854 | ||
| 855 | The "procs_running" line gives the number of processes currently running on | |
| 856 | CPUs. | |
| 857 | ||
| 858 | The "procs_blocked" line gives the number of processes currently blocked, | |
| 859 | waiting for I/O to complete. | |
| 860 | ||
| c9de560d AT |
861 | 1.9 Ext4 file system parameters |
| 862 | ------------------------------ | |
| 863 | Ext4 file system have one directory per partition under /proc/fs/ext4/ | |
| 864 | # ls /proc/fs/ext4/hdc/ | |
| 865 | group_prealloc max_to_scan mb_groups mb_history min_to_scan order2_req | |
| 866 | stats stream_req | |
| 867 | ||
| 868 | mb_groups: | |
| 869 | This file gives the details of mutiblock allocator buddy cache of free blocks | |
| 870 | ||
| 871 | mb_history: | |
| 872 | Multiblock allocation history. | |
| 873 | ||
| 874 | stats: | |
| 875 | This file indicate whether the multiblock allocator should start collecting | |
| 876 | statistics. The statistics are shown during unmount | |
| 877 | ||
| 878 | group_prealloc: | |
| 879 | The multiblock allocator normalize the block allocation request to | |
| 880 | group_prealloc filesystem blocks if we don't have strip value set. | |
| 881 | The stripe value can be specified at mount time or during mke2fs. | |
| 882 | ||
| 883 | max_to_scan: | |
| 884 | How long multiblock allocator can look for a best extent (in found extents) | |
| 885 | ||
| 886 | min_to_scan: | |
| 887 | How long multiblock allocator must look for a best extent | |
| 888 | ||
| 889 | order2_req: | |
| 890 | Multiblock allocator use 2^N search using buddies only for requests greater | |
| 891 | than or equal to order2_req. The request size is specfied in file system | |
| 892 | blocks. A value of 2 indicate only if the requests are greater than or equal | |
| 893 | to 4 blocks. | |
| 894 | ||
| 895 | stream_req: | |
| 896 | Files smaller than stream_req are served by the stream allocator, whose | |
| 897 | purpose is to pack requests as close each to other as possible to | |
| 898 | produce smooth I/O traffic. Avalue of 16 indicate that file smaller than 16 | |
| 899 | filesystem block size will use group based preallocation. | |
| 1da177e4 LT |
900 | |
| 901 | ------------------------------------------------------------------------------ | |
| 902 | Summary | |
| 903 | ------------------------------------------------------------------------------ | |
| 904 | The /proc file system serves information about the running system. It not only | |
| 905 | allows access to process data but also allows you to request the kernel status | |
| 906 | by reading files in the hierarchy. | |
| 907 | ||
| 908 | The directory structure of /proc reflects the types of information and makes | |
| 909 | it easy, if not obvious, where to look for specific data. | |
| 910 | ------------------------------------------------------------------------------ | |
| 911 | ||
| 912 | ------------------------------------------------------------------------------ | |
| 913 | CHAPTER 2: MODIFYING SYSTEM PARAMETERS | |
| 914 | ------------------------------------------------------------------------------ | |
| 915 | ||
| 916 | ------------------------------------------------------------------------------ | |
| 917 | In This Chapter | |
| 918 | ------------------------------------------------------------------------------ | |
| 919 | * Modifying kernel parameters by writing into files found in /proc/sys | |
| 920 | * Exploring the files which modify certain parameters | |
| 921 | * Review of the /proc/sys file tree | |
| 922 | ------------------------------------------------------------------------------ | |
| 923 | ||
| 924 | ||
| 925 | A very interesting part of /proc is the directory /proc/sys. This is not only | |
| 926 | a source of information, it also allows you to change parameters within the | |
| 927 | kernel. Be very careful when attempting this. You can optimize your system, | |
| 928 | but you can also cause it to crash. Never alter kernel parameters on a | |
| 929 | production system. Set up a development machine and test to make sure that | |
| 930 | everything works the way you want it to. You may have no alternative but to | |
| 931 | reboot the machine once an error has been made. | |
| 932 | ||
| 933 | To change a value, simply echo the new value into the file. An example is | |
| 934 | given below in the section on the file system data. You need to be root to do | |
| 935 | this. You can create your own boot script to perform this every time your | |
| 936 | system boots. | |
| 937 | ||
| 938 | The files in /proc/sys can be used to fine tune and monitor miscellaneous and | |
| 939 | general things in the operation of the Linux kernel. Since some of the files | |
| 940 | can inadvertently disrupt your system, it is advisable to read both | |
| 941 | documentation and source before actually making adjustments. In any case, be | |
| 942 | very careful when writing to any of these files. The entries in /proc may | |
| 943 | change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt | |
| 944 | review the kernel documentation in the directory /usr/src/linux/Documentation. | |
| 945 | This chapter is heavily based on the documentation included in the pre 2.2 | |
| 946 | kernels, and became part of it in version 2.2.1 of the Linux kernel. | |
| 947 | ||
| 948 | 2.1 /proc/sys/fs - File system data | |
| 949 | ----------------------------------- | |
| 950 | ||
| 951 | This subdirectory contains specific file system, file handle, inode, dentry | |
| 952 | and quota information. | |
| 953 | ||
| 954 | Currently, these files are in /proc/sys/fs: | |
| 955 | ||
| 956 | dentry-state | |
| 957 | ------------ | |
| 958 | ||
| 959 | Status of the directory cache. Since directory entries are dynamically | |
| 960 | allocated and deallocated, this file indicates the current status. It holds | |
| 961 | six values, in which the last two are not used and are always zero. The others | |
| 962 | are listed in table 2-1. | |
| 963 | ||
| 964 | ||
| 965 | Table 2-1: Status files of the directory cache | |
| 966 | .............................................................................. | |
| 967 | File Content | |
| 968 | nr_dentry Almost always zero | |
| 969 | nr_unused Number of unused cache entries | |
| 970 | age_limit | |
| 971 | in seconds after the entry may be reclaimed, when memory is short | |
| 972 | want_pages internally | |
| 973 | .............................................................................. | |
| 974 | ||
| 975 | dquot-nr and dquot-max | |
| 976 | ---------------------- | |
| 977 | ||
| 978 | The file dquot-max shows the maximum number of cached disk quota entries. | |
| 979 | ||
| 980 | The file dquot-nr shows the number of allocated disk quota entries and the | |
| 981 | number of free disk quota entries. | |
| 982 | ||
| 983 | If the number of available cached disk quotas is very low and you have a large | |
| 984 | number of simultaneous system users, you might want to raise the limit. | |
| 985 | ||
| 986 | file-nr and file-max | |
| 987 | -------------------- | |
| 988 | ||
| 989 | The kernel allocates file handles dynamically, but doesn't free them again at | |
| 990 | this time. | |
| 991 | ||
| 992 | The value in file-max denotes the maximum number of file handles that the | |
| 993 | Linux kernel will allocate. When you get a lot of error messages about running | |
| 994 | out of file handles, you might want to raise this limit. The default value is | |
| 995 | 10% of RAM in kilobytes. To change it, just write the new number into the | |
| 996 | file: | |
| 997 | ||
| 998 | # cat /proc/sys/fs/file-max | |
| 999 | 4096 | |
| 1000 | # echo 8192 > /proc/sys/fs/file-max | |
| 1001 | # cat /proc/sys/fs/file-max | |
| 1002 | 8192 | |
| 1003 | ||
| 1004 | ||
| 1005 | This method of revision is useful for all customizable parameters of the | |
| 1006 | kernel - simply echo the new value to the corresponding file. | |
| 1007 | ||
| 1008 | Historically, the three values in file-nr denoted the number of allocated file | |
| 1009 | handles, the number of allocated but unused file handles, and the maximum | |
| 1010 | number of file handles. Linux 2.6 always reports 0 as the number of free file | |
| 1011 | handles -- this is not an error, it just means that the number of allocated | |
| 1012 | file handles exactly matches the number of used file handles. | |
| 1013 | ||
| 1014 | Attempts to allocate more file descriptors than file-max are reported with | |
| 1015 | printk, look for "VFS: file-max limit <number> reached". | |
| 1016 | ||
| 1017 | inode-state and inode-nr | |
| 1018 | ------------------------ | |
| 1019 | ||
| 1020 | The file inode-nr contains the first two items from inode-state, so we'll skip | |
| 1021 | to that file... | |
| 1022 | ||
| 1023 | inode-state contains two actual numbers and five dummy values. The numbers | |
| 1024 | are nr_inodes and nr_free_inodes (in order of appearance). | |
| 1025 | ||
| 1026 | nr_inodes | |
| 1027 | ~~~~~~~~~ | |
| 1028 | ||
| 1029 | Denotes the number of inodes the system has allocated. This number will | |
| 1030 | grow and shrink dynamically. | |
| 1031 | ||
| 9cfe015a ED |
1032 | nr_open |
| 1033 | ------- | |
| 1034 | ||
| 1035 | Denotes the maximum number of file-handles a process can | |
| 1036 | allocate. Default value is 1024*1024 (1048576) which should be | |
| 1037 | enough for most machines. Actual limit depends on RLIMIT_NOFILE | |
| 1038 | resource limit. | |
| 1039 | ||
| 1da177e4 LT |
1040 | nr_free_inodes |
| 1041 | -------------- | |
| 1042 | ||
| 1043 | Represents the number of free inodes. Ie. The number of inuse inodes is | |
| 1044 | (nr_inodes - nr_free_inodes). | |
| 1045 | ||
| 1da177e4 LT |
1046 | aio-nr and aio-max-nr |
| 1047 | --------------------- | |
| 1048 | ||
| 1049 | aio-nr is the running total of the number of events specified on the | |
| 1050 | io_setup system call for all currently active aio contexts. If aio-nr | |
| 1051 | reaches aio-max-nr then io_setup will fail with EAGAIN. Note that | |
| 1052 | raising aio-max-nr does not result in the pre-allocation or re-sizing | |
| 1053 | of any kernel data structures. | |
| 1054 | ||
| 1055 | 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats | |
| 1056 | ----------------------------------------------------------- | |
| 1057 | ||
| 1058 | Besides these files, there is the subdirectory /proc/sys/fs/binfmt_misc. This | |
| 1059 | handles the kernel support for miscellaneous binary formats. | |
| 1060 | ||
| 1061 | Binfmt_misc provides the ability to register additional binary formats to the | |
| 1062 | Kernel without compiling an additional module/kernel. Therefore, binfmt_misc | |
| 1063 | needs to know magic numbers at the beginning or the filename extension of the | |
| 1064 | binary. | |
| 1065 | ||
| 1066 | It works by maintaining a linked list of structs that contain a description of | |
| 1067 | a binary format, including a magic with size (or the filename extension), | |
| 1068 | offset and mask, and the interpreter name. On request it invokes the given | |
| 1069 | interpreter with the original program as argument, as binfmt_java and | |
| 1070 | binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default | |
| 1071 | binary-formats, you have to register an additional binary-format. | |
| 1072 | ||
| 1073 | There are two general files in binfmt_misc and one file per registered format. | |
| 1074 | The two general files are register and status. | |
| 1075 | ||
| 1076 | Registering a new binary format | |
| 1077 | ------------------------------- | |
| 1078 | ||
| 1079 | To register a new binary format you have to issue the command | |
| 1080 | ||
| 1081 | echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register | |
| 1082 | ||
| 1083 | ||
| 1084 | ||
| 1085 | with appropriate name (the name for the /proc-dir entry), offset (defaults to | |
| 1086 | 0, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and | |
| 1087 | last but not least, the interpreter that is to be invoked (for example and | |
| 1088 | testing /bin/echo). Type can be M for usual magic matching or E for filename | |
| 1089 | extension matching (give extension in place of magic). | |
| 1090 | ||
| 1091 | Check or reset the status of the binary format handler | |
| 1092 | ------------------------------------------------------ | |
| 1093 | ||
| 1094 | If you do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the | |
| 1095 | current status (enabled/disabled) of binfmt_misc. Change the status by echoing | |
| 1096 | 0 (disables) or 1 (enables) or -1 (caution: this clears all previously | |
| 1097 | registered binary formats) to status. For example echo 0 > status to disable | |
| 1098 | binfmt_misc (temporarily). | |
| 1099 | ||
| 1100 | Status of a single handler | |
| 1101 | -------------------------- | |
| 1102 | ||
| 1103 | Each registered handler has an entry in /proc/sys/fs/binfmt_misc. These files | |
| 1104 | perform the same function as status, but their scope is limited to the actual | |
| 1105 | binary format. By cating this file, you also receive all related information | |
| 1106 | about the interpreter/magic of the binfmt. | |
| 1107 | ||
| 1108 | Example usage of binfmt_misc (emulate binfmt_java) | |
| 1109 | -------------------------------------------------- | |
| 1110 | ||
| 1111 | cd /proc/sys/fs/binfmt_misc | |
| 1112 | echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register | |
| 1113 | echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register | |
| 1114 | echo ':Applet:M::<!--applet::/usr/local/java/bin/appletviewer:' > register | |
| 1115 | echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register | |
| 1116 | ||
| 1117 | ||
| 1118 | These four lines add support for Java executables and Java applets (like | |
| 1119 | binfmt_java, additionally recognizing the .html extension with no need to put | |
| 1120 | <!--applet> to every applet file). You have to install the JDK and the | |
| 1121 | shell-script /usr/local/java/bin/javawrapper too. It works around the | |
| 1122 | brokenness of the Java filename handling. To add a Java binary, just create a | |
| 1123 | link to the class-file somewhere in the path. | |
| 1124 | ||
| 1125 | 2.3 /proc/sys/kernel - general kernel parameters | |
| 1126 | ------------------------------------------------ | |
| 1127 | ||
| 1128 | This directory reflects general kernel behaviors. As I've said before, the | |
| 1129 | contents depend on your configuration. Here you'll find the most important | |
| 1130 | files, along with descriptions of what they mean and how to use them. | |
| 1131 | ||
| 1132 | acct | |
| 1133 | ---- | |
| 1134 | ||
| 1135 | The file contains three values; highwater, lowwater, and frequency. | |
| 1136 | ||
| 1137 | It exists only when BSD-style process accounting is enabled. These values | |
| 1138 | control its behavior. If the free space on the file system where the log lives | |
| 1139 | goes below lowwater percentage, accounting suspends. If it goes above | |
| 1140 | highwater percentage, accounting resumes. Frequency determines how often you | |
| 1141 | check the amount of free space (value is in seconds). Default settings are: 4, | |
| 1142 | 2, and 30. That is, suspend accounting if there is less than 2 percent free; | |
| 1143 | resume it if we have a value of 3 or more percent; consider information about | |
| 1144 | the amount of free space valid for 30 seconds | |
| 1145 | ||
| 1146 | ctrl-alt-del | |
| 1147 | ------------ | |
| 1148 | ||
| 1149 | When the value in this file is 0, ctrl-alt-del is trapped and sent to the init | |
| 1150 | program to handle a graceful restart. However, when the value is greater that | |
| 1151 | zero, Linux's reaction to this key combination will be an immediate reboot, | |
| 1152 | without syncing its dirty buffers. | |
| 1153 | ||
| 1154 | [NOTE] | |
| 1155 | When a program (like dosemu) has the keyboard in raw mode, the | |
| 1156 | ctrl-alt-del is intercepted by the program before it ever reaches the | |
| 1157 | kernel tty layer, and it is up to the program to decide what to do with | |
| 1158 | it. | |
| 1159 | ||
| 1160 | domainname and hostname | |
| 1161 | ----------------------- | |
| 1162 | ||
| 1163 | These files can be controlled to set the NIS domainname and hostname of your | |
| 1164 | box. For the classic darkstar.frop.org a simple: | |
| 1165 | ||
| 1166 | # echo "darkstar" > /proc/sys/kernel/hostname | |
| 1167 | # echo "frop.org" > /proc/sys/kernel/domainname | |
| 1168 | ||
| 1169 | ||
| 1170 | would suffice to set your hostname and NIS domainname. | |
| 1171 | ||
| 1172 | osrelease, ostype and version | |
| 1173 | ----------------------------- | |
| 1174 | ||
| 1175 | The names make it pretty obvious what these fields contain: | |
| 1176 | ||
| 1177 | > cat /proc/sys/kernel/osrelease | |
| 1178 | 2.2.12 | |
| 1179 | ||
| 1180 | > cat /proc/sys/kernel/ostype | |
| 1181 | Linux | |
| 1182 | ||
| 1183 | > cat /proc/sys/kernel/version | |
| 1184 | #4 Fri Oct 1 12:41:14 PDT 1999 | |
| 1185 | ||
| 1186 | ||
| 1187 | The files osrelease and ostype should be clear enough. Version needs a little | |
| 1188 | more clarification. The #4 means that this is the 4th kernel built from this | |
| 1189 | source base and the date after it indicates the time the kernel was built. The | |
| 1190 | only way to tune these values is to rebuild the kernel. | |
| 1191 | ||
| 1192 | panic | |
| 1193 | ----- | |
| 1194 | ||
| 1195 | The value in this file represents the number of seconds the kernel waits | |
| 1196 | before rebooting on a panic. When you use the software watchdog, the | |
| 1197 | recommended setting is 60. If set to 0, the auto reboot after a kernel panic | |
| 1198 | is disabled, which is the default setting. | |
| 1199 | ||
| 1200 | printk | |
| 1201 | ------ | |
| 1202 | ||
| 1203 | The four values in printk denote | |
| 1204 | * console_loglevel, | |
| 1205 | * default_message_loglevel, | |
| 1206 | * minimum_console_loglevel and | |
| 1207 | * default_console_loglevel | |
| 1208 | respectively. | |
| 1209 | ||
| 1210 | These values influence printk() behavior when printing or logging error | |
| 1211 | messages, which come from inside the kernel. See syslog(2) for more | |
| 1212 | information on the different log levels. | |
| 1213 | ||
| 1214 | console_loglevel | |
| 1215 | ---------------- | |
| 1216 | ||
| 1217 | Messages with a higher priority than this will be printed to the console. | |
| 1218 | ||
| 1219 | default_message_level | |
| 1220 | --------------------- | |
| 1221 | ||
| 1222 | Messages without an explicit priority will be printed with this priority. | |
| 1223 | ||
| 1224 | minimum_console_loglevel | |
| 1225 | ------------------------ | |
| 1226 | ||
| 1227 | Minimum (highest) value to which the console_loglevel can be set. | |
| 1228 | ||
| 1229 | default_console_loglevel | |
| 1230 | ------------------------ | |
| 1231 | ||
| 1232 | Default value for console_loglevel. | |
| 1233 | ||
| 1234 | sg-big-buff | |
| 1235 | ----------- | |
| 1236 | ||
| 1237 | This file shows the size of the generic SCSI (sg) buffer. At this point, you | |
| 1238 | can't tune it yet, but you can change it at compile time by editing | |
| 1239 | include/scsi/sg.h and changing the value of SG_BIG_BUFF. | |
| 1240 | ||
| 1241 | If you use a scanner with SANE (Scanner Access Now Easy) you might want to set | |
| 1242 | this to a higher value. Refer to the SANE documentation on this issue. | |
| 1243 | ||
| 1244 | modprobe | |
| 1245 | -------- | |
| 1246 | ||
| 1247 | The location where the modprobe binary is located. The kernel uses this | |
| 1248 | program to load modules on demand. | |
| 1249 | ||
| 1250 | unknown_nmi_panic | |
| 1251 | ----------------- | |
| 1252 | ||
| 1253 | The value in this file affects behavior of handling NMI. When the value is | |
| 1254 | non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel | |
| 1255 | debugging information is displayed on console. | |
| 1256 | ||
| 1257 | NMI switch that most IA32 servers have fires unknown NMI up, for example. | |
| 1258 | If a system hangs up, try pressing the NMI switch. | |
| 1259 | ||
| e33e89ab DZ |
1260 | nmi_watchdog |
| 1261 | ------------ | |
| 1262 | ||
| 1263 | Enables/Disables the NMI watchdog on x86 systems. When the value is non-zero | |
| 1264 | the NMI watchdog is enabled and will continuously test all online cpus to | |
| 1265 | determine whether or not they are still functioning properly. | |
| 1266 | ||
| 1267 | Because the NMI watchdog shares registers with oprofile, by disabling the NMI | |
| 1268 | watchdog, oprofile may have more registers to utilize. | |
| 1da177e4 | 1269 | |
| 5096add8 KC |
1270 | maps_protect |
| 1271 | ------------ | |
| 1272 | ||
| 1273 | Enables/Disables the protection of the per-process proc entries "maps" and | |
| 1274 | "smaps". When enabled, the contents of these files are visible only to | |
| 1275 | readers that are allowed to ptrace() the given process. | |
| 1276 | ||
| 1da177e4 LT |
1277 | |
| 1278 | 2.4 /proc/sys/vm - The virtual memory subsystem | |
| 1279 | ----------------------------------------------- | |
| 1280 | ||
| 1281 | The files in this directory can be used to tune the operation of the virtual | |
| 1282 | memory (VM) subsystem of the Linux kernel. | |
| 1283 | ||
| 1284 | vfs_cache_pressure | |
| 1285 | ------------------ | |
| 1286 | ||
| 1287 | Controls the tendency of the kernel to reclaim the memory which is used for | |
| 1288 | caching of directory and inode objects. | |
| 1289 | ||
| 1290 | At the default value of vfs_cache_pressure=100 the kernel will attempt to | |
| 1291 | reclaim dentries and inodes at a "fair" rate with respect to pagecache and | |
| 1292 | swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer | |
| 1293 | to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100 | |
| 1294 | causes the kernel to prefer to reclaim dentries and inodes. | |
| 1295 | ||
| 1296 | dirty_background_ratio | |
| 1297 | ---------------------- | |
| 1298 | ||
| 1299 | Contains, as a percentage of total system memory, the number of pages at which | |
| 1300 | the pdflush background writeback daemon will start writing out dirty data. | |
| 1301 | ||
| 1302 | dirty_ratio | |
| 1303 | ----------------- | |
| 1304 | ||
| 1305 | Contains, as a percentage of total system memory, the number of pages at which | |
| 1306 | a process which is generating disk writes will itself start writing out dirty | |
| 1307 | data. | |
| 1308 | ||
| 1309 | dirty_writeback_centisecs | |
| 1310 | ------------------------- | |
| 1311 | ||
| 1312 | The pdflush writeback daemons will periodically wake up and write `old' data | |
| 1313 | out to disk. This tunable expresses the interval between those wakeups, in | |
| 1314 | 100'ths of a second. | |
| 1315 | ||
| 1316 | Setting this to zero disables periodic writeback altogether. | |
| 1317 | ||
| 1318 | dirty_expire_centisecs | |
| 1319 | ---------------------- | |
| 1320 | ||
| 1321 | This tunable is used to define when dirty data is old enough to be eligible | |
| 1322 | for writeout by the pdflush daemons. It is expressed in 100'ths of a second. | |
| 1323 | Data which has been dirty in-memory for longer than this interval will be | |
| 1324 | written out next time a pdflush daemon wakes up. | |
| 1325 | ||
| 195cf453 BG |
1326 | highmem_is_dirtyable |
| 1327 | -------------------- | |
| 1328 | ||
| 1329 | Only present if CONFIG_HIGHMEM is set. | |
| 1330 | ||
| 1331 | This defaults to 0 (false), meaning that the ratios set above are calculated | |
| 1332 | as a percentage of lowmem only. This protects against excessive scanning | |
| 1333 | in page reclaim, swapping and general VM distress. | |
| 1334 | ||
| 1335 | Setting this to 1 can be useful on 32 bit machines where you want to make | |
| 1336 | random changes within an MMAPed file that is larger than your available | |
| 1337 | lowmem without causing large quantities of random IO. Is is safe if the | |
| 1338 | behavior of all programs running on the machine is known and memory will | |
| 1339 | not be otherwise stressed. | |
| 1340 | ||
| 1da177e4 LT |
1341 | legacy_va_layout |
| 1342 | ---------------- | |
| 1343 | ||
| 1344 | If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel | |
| 1345 | will use the legacy (2.4) layout for all processes. | |
| 1346 | ||
| 7786fa9a | 1347 | lowmem_reserve_ratio |
| 1da177e4 LT |
1348 | --------------------- |
| 1349 | ||
| 1350 | For some specialised workloads on highmem machines it is dangerous for | |
| 1351 | the kernel to allow process memory to be allocated from the "lowmem" | |
| 1352 | zone. This is because that memory could then be pinned via the mlock() | |
| 1353 | system call, or by unavailability of swapspace. | |
| 1354 | ||
| 1355 | And on large highmem machines this lack of reclaimable lowmem memory | |
| 1356 | can be fatal. | |
| 1357 | ||
| 1358 | So the Linux page allocator has a mechanism which prevents allocations | |
| 1359 | which _could_ use highmem from using too much lowmem. This means that | |
| 1360 | a certain amount of lowmem is defended from the possibility of being | |
| 1361 | captured into pinned user memory. | |
| 1362 | ||
| 1363 | (The same argument applies to the old 16 megabyte ISA DMA region. This | |
| 1364 | mechanism will also defend that region from allocations which could use | |
| 1365 | highmem or lowmem). | |
| 1366 | ||
| 7786fa9a YG |
1367 | The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is |
| 1368 | in defending these lower zones. | |
| 1da177e4 LT |
1369 | |
| 1370 | If you have a machine which uses highmem or ISA DMA and your | |
| 1371 | applications are using mlock(), or if you are running with no swap then | |
| 7786fa9a YG |
1372 | you probably should change the lowmem_reserve_ratio setting. |
| 1373 | ||
| 1374 | The lowmem_reserve_ratio is an array. You can see them by reading this file. | |
| 1375 | - | |
| 1376 | % cat /proc/sys/vm/lowmem_reserve_ratio | |
| 1377 | 256 256 32 | |
| 1378 | - | |
| 1379 | Note: # of this elements is one fewer than number of zones. Because the highest | |
| 1380 | zone's value is not necessary for following calculation. | |
| 1381 | ||
| 1382 | But, these values are not used directly. The kernel calculates # of protection | |
| 1383 | pages for each zones from them. These are shown as array of protection pages | |
| 1384 | in /proc/zoneinfo like followings. (This is an example of x86-64 box). | |
| 1385 | Each zone has an array of protection pages like this. | |
| 1386 | ||
| 1387 | - | |
| 1388 | Node 0, zone DMA | |
| 1389 | pages free 1355 | |
| 1390 | min 3 | |
| 1391 | low 3 | |
| 1392 | high 4 | |
| 1393 | : | |
| 1394 | : | |
| 1395 | numa_other 0 | |
| 1396 | protection: (0, 2004, 2004, 2004) | |
| 1397 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
| 1398 | pagesets | |
| 1399 | cpu: 0 pcp: 0 | |
| 1400 | : | |
| 1401 | - | |
| 1402 | These protections are added to score to judge whether this zone should be used | |
| 1403 | for page allocation or should be reclaimed. | |
| 1404 | ||
| 1405 | In this example, if normal pages (index=2) are required to this DMA zone and | |
| 1406 | pages_high is used for watermark, the kernel judges this zone should not be | |
| 1407 | used because pages_free(1355) is smaller than watermark + protection[2] | |
| 1408 | (4 + 2004 = 2008). If this protection value is 0, this zone would be used for | |
| 1409 | normal page requirement. If requirement is DMA zone(index=0), protection[0] | |
| 1410 | (=0) is used. | |
| 1411 | ||
| 1412 | zone[i]'s protection[j] is calculated by following exprssion. | |
| 1413 | ||
| 1414 | (i < j): | |
| 1415 | zone[i]->protection[j] | |
| 1416 | = (total sums of present_pages from zone[i+1] to zone[j] on the node) | |
| 1417 | / lowmem_reserve_ratio[i]; | |
| 1418 | (i = j): | |
| 1419 | (should not be protected. = 0; | |
| 1420 | (i > j): | |
| 1421 | (not necessary, but looks 0) | |
| 1422 | ||
| 1423 | The default values of lowmem_reserve_ratio[i] are | |
| 1424 | 256 (if zone[i] means DMA or DMA32 zone) | |
| 1425 | 32 (others). | |
| 1426 | As above expression, they are reciprocal number of ratio. | |
| 1427 | 256 means 1/256. # of protection pages becomes about "0.39%" of total present | |
| 1428 | pages of higher zones on the node. | |
| 1429 | ||
| 1430 | If you would like to protect more pages, smaller values are effective. | |
| 1431 | The minimum value is 1 (1/1 -> 100%). | |
| 1da177e4 LT |
1432 | |
| 1433 | page-cluster | |
| 1434 | ------------ | |
| 1435 | ||
| 1436 | page-cluster controls the number of pages which are written to swap in | |
| 1437 | a single attempt. The swap I/O size. | |
| 1438 | ||
| 1439 | It is a logarithmic value - setting it to zero means "1 page", setting | |
| 1440 | it to 1 means "2 pages", setting it to 2 means "4 pages", etc. | |
| 1441 | ||
| 1442 | The default value is three (eight pages at a time). There may be some | |
| 1443 | small benefits in tuning this to a different value if your workload is | |
| 1444 | swap-intensive. | |
| 1445 | ||
| 1446 | overcommit_memory | |
| 1447 | ----------------- | |
| 1448 | ||
| af97c722 CE |
1449 | Controls overcommit of system memory, possibly allowing processes |
| 1450 | to allocate (but not use) more memory than is actually available. | |
| 1451 | ||
| 1452 | ||
| 1453 | 0 - Heuristic overcommit handling. Obvious overcommits of | |
| 1454 | address space are refused. Used for a typical system. It | |
| 1455 | ensures a seriously wild allocation fails while allowing | |
| 1456 | overcommit to reduce swap usage. root is allowed to | |
| 53cb4726 | 1457 | allocate slightly more memory in this mode. This is the |
| af97c722 CE |
1458 | default. |
| 1459 | ||
| 1460 | 1 - Always overcommit. Appropriate for some scientific | |
| 1461 | applications. | |
| 1462 | ||
| 1463 | 2 - Don't overcommit. The total address space commit | |
| 1464 | for the system is not permitted to exceed swap plus a | |
| 1465 | configurable percentage (default is 50) of physical RAM. | |
| 1466 | Depending on the percentage you use, in most situations | |
| 1467 | this means a process will not be killed while attempting | |
| 1468 | to use already-allocated memory but will receive errors | |
| 1469 | on memory allocation as appropriate. | |
| 1470 | ||
| 1471 | overcommit_ratio | |
| 1472 | ---------------- | |
| 1473 | ||
| 1474 | Percentage of physical memory size to include in overcommit calculations | |
| 1475 | (see above.) | |
| 1476 | ||
| 1477 | Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100) | |
| 1478 | ||
| 1479 | swapspace = total size of all swap areas | |
| 1480 | physmem = size of physical memory in system | |
| 1da177e4 LT |
1481 | |
| 1482 | nr_hugepages and hugetlb_shm_group | |
| 1483 | ---------------------------------- | |
| 1484 | ||
| 1485 | nr_hugepages configures number of hugetlb page reserved for the system. | |
| 1486 | ||
| 1487 | hugetlb_shm_group contains group id that is allowed to create SysV shared | |
| 1488 | memory segment using hugetlb page. | |
| 1489 | ||
| ed7ed365 MG |
1490 | hugepages_treat_as_movable |
| 1491 | -------------------------- | |
| 1492 | ||
| 1493 | This parameter is only useful when kernelcore= is specified at boot time to | |
| 1494 | create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages | |
| 1495 | are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero | |
| 1496 | value written to hugepages_treat_as_movable allows huge pages to be allocated | |
| 1497 | from ZONE_MOVABLE. | |
| 1498 | ||
| 1499 | Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge | |
| 1500 | pages pool can easily grow or shrink within. Assuming that applications are | |
| 1501 | not running that mlock() a lot of memory, it is likely the huge pages pool | |
| 1502 | can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value | |
| 1503 | into nr_hugepages and triggering page reclaim. | |
| 1504 | ||
| 1da177e4 LT |
1505 | laptop_mode |
| 1506 | ----------- | |
| 1507 | ||
| 1508 | laptop_mode is a knob that controls "laptop mode". All the things that are | |
| a09a20b5 | 1509 | controlled by this knob are discussed in Documentation/laptops/laptop-mode.txt. |
| 1da177e4 LT |
1510 | |
| 1511 | block_dump | |
| 1512 | ---------- | |
| 1513 | ||
| 1514 | block_dump enables block I/O debugging when set to a nonzero value. More | |
| a09a20b5 | 1515 | information on block I/O debugging is in Documentation/laptops/laptop-mode.txt. |
| 1da177e4 LT |
1516 | |
| 1517 | swap_token_timeout | |
| 1518 | ------------------ | |
| 1519 | ||
| 1520 | This file contains valid hold time of swap out protection token. The Linux | |
| 1521 | VM has token based thrashing control mechanism and uses the token to prevent | |
| 1522 | unnecessary page faults in thrashing situation. The unit of the value is | |
| 1523 | second. The value would be useful to tune thrashing behavior. | |
| 1524 | ||
| 9d0243bc AM |
1525 | drop_caches |
| 1526 | ----------- | |
| 1527 | ||
| 1528 | Writing to this will cause the kernel to drop clean caches, dentries and | |
| 1529 | inodes from memory, causing that memory to become free. | |
| 1530 | ||
| 1531 | To free pagecache: | |
| 1532 | echo 1 > /proc/sys/vm/drop_caches | |
| 1533 | To free dentries and inodes: | |
| 1534 | echo 2 > /proc/sys/vm/drop_caches | |
| 1535 | To free pagecache, dentries and inodes: | |
| 1536 | echo 3 > /proc/sys/vm/drop_caches | |
| 1537 | ||
| 1538 | As this is a non-destructive operation and dirty objects are not freeable, the | |
| 1539 | user should run `sync' first. | |
| 1540 | ||
| 1541 | ||
| 1da177e4 LT |
1542 | 2.5 /proc/sys/dev - Device specific parameters |
| 1543 | ---------------------------------------------- | |
| 1544 | ||
| 1545 | Currently there is only support for CDROM drives, and for those, there is only | |
| 1546 | one read-only file containing information about the CD-ROM drives attached to | |
| 1547 | the system: | |
| 1548 | ||
| 1549 | >cat /proc/sys/dev/cdrom/info | |
| 1550 | CD-ROM information, Id: cdrom.c 2.55 1999/04/25 | |
| 1551 | ||
| 1552 | drive name: sr0 hdb | |
| 1553 | drive speed: 32 40 | |
| 1554 | drive # of slots: 1 0 | |
| 1555 | Can close tray: 1 1 | |
| 1556 | Can open tray: 1 1 | |
| 1557 | Can lock tray: 1 1 | |
| 1558 | Can change speed: 1 1 | |
| 1559 | Can select disk: 0 1 | |
| 1560 | Can read multisession: 1 1 | |
| 1561 | Can read MCN: 1 1 | |
| 1562 | Reports media changed: 1 1 | |
| 1563 | Can play audio: 1 1 | |
| 1564 | ||
| 1565 | ||
| 1566 | You see two drives, sr0 and hdb, along with a list of their features. | |
| 1567 | ||
| 1568 | 2.6 /proc/sys/sunrpc - Remote procedure calls | |
| 1569 | --------------------------------------------- | |
| 1570 | ||
| 1571 | This directory contains four files, which enable or disable debugging for the | |
| 1572 | RPC functions NFS, NFS-daemon, RPC and NLM. The default values are 0. They can | |
| 1573 | be set to one to turn debugging on. (The default value is 0 for each) | |
| 1574 | ||
| 1575 | 2.7 /proc/sys/net - Networking stuff | |
| 1576 | ------------------------------------ | |
| 1577 | ||
| 1578 | The interface to the networking parts of the kernel is located in | |
| 1579 | /proc/sys/net. Table 2-3 shows all possible subdirectories. You may see only | |
| 1580 | some of them, depending on your kernel's configuration. | |
| 1581 | ||
| 1582 | ||
| 1583 | Table 2-3: Subdirectories in /proc/sys/net | |
| 1584 | .............................................................................. | |
| 1585 | Directory Content Directory Content | |
| 1586 | core General parameter appletalk Appletalk protocol | |
| 1587 | unix Unix domain sockets netrom NET/ROM | |
| 1588 | 802 E802 protocol ax25 AX25 | |
| 1589 | ethernet Ethernet protocol rose X.25 PLP layer | |
| 1590 | ipv4 IP version 4 x25 X.25 protocol | |
| 1591 | ipx IPX token-ring IBM token ring | |
| 1592 | bridge Bridging decnet DEC net | |
| 1593 | ipv6 IP version 6 | |
| 1594 | .............................................................................. | |
| 1595 | ||
| 1596 | We will concentrate on IP networking here. Since AX15, X.25, and DEC Net are | |
| 1597 | only minor players in the Linux world, we'll skip them in this chapter. You'll | |
| 1598 | find some short info on Appletalk and IPX further on in this chapter. Review | |
| 1599 | the online documentation and the kernel source to get a detailed view of the | |
| 1600 | parameters for those protocols. In this section we'll discuss the | |
| 1601 | subdirectories printed in bold letters in the table above. As default values | |
| 1602 | are suitable for most needs, there is no need to change these values. | |
| 1603 | ||
| 1604 | /proc/sys/net/core - Network core options | |
| 1605 | ----------------------------------------- | |
| 1606 | ||
| 1607 | rmem_default | |
| 1608 | ------------ | |
| 1609 | ||
| 1610 | The default setting of the socket receive buffer in bytes. | |
| 1611 | ||
| 1612 | rmem_max | |
| 1613 | -------- | |
| 1614 | ||
| 1615 | The maximum receive socket buffer size in bytes. | |
| 1616 | ||
| 1617 | wmem_default | |
| 1618 | ------------ | |
| 1619 | ||
| 1620 | The default setting (in bytes) of the socket send buffer. | |
| 1621 | ||
| 1622 | wmem_max | |
| 1623 | -------- | |
| 1624 | ||
| 1625 | The maximum send socket buffer size in bytes. | |
| 1626 | ||
| 1627 | message_burst and message_cost | |
| 1628 | ------------------------------ | |
| 1629 | ||
| 1630 | These parameters are used to limit the warning messages written to the kernel | |
| 1631 | log from the networking code. They enforce a rate limit to make a | |
| 1632 | denial-of-service attack impossible. A higher message_cost factor, results in | |
| 1633 | fewer messages that will be written. Message_burst controls when messages will | |
| 1634 | be dropped. The default settings limit warning messages to one every five | |
| 1635 | seconds. | |
| 1636 | ||
| a2a316fd SH |
1637 | warnings |
| 1638 | -------- | |
| 1639 | ||
| 1640 | This controls console messages from the networking stack that can occur because | |
| 1641 | of problems on the network like duplicate address or bad checksums. Normally, | |
| 1642 | this should be enabled, but if the problem persists the messages can be | |
| 1643 | disabled. | |
| 1644 | ||
| 1645 | ||
| 1da177e4 LT |
1646 | netdev_max_backlog |
| 1647 | ------------------ | |
| 1648 | ||
| 1649 | Maximum number of packets, queued on the INPUT side, when the interface | |
| 1650 | receives packets faster than kernel can process them. | |
| 1651 | ||
| 1652 | optmem_max | |
| 1653 | ---------- | |
| 1654 | ||
| 1655 | Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence | |
| 1656 | of struct cmsghdr structures with appended data. | |
| 1657 | ||
| 1658 | /proc/sys/net/unix - Parameters for Unix domain sockets | |
| 1659 | ------------------------------------------------------- | |
| 1660 | ||
| 1661 | There are only two files in this subdirectory. They control the delays for | |
| 1662 | deleting and destroying socket descriptors. | |
| 1663 | ||
| 1664 | 2.8 /proc/sys/net/ipv4 - IPV4 settings | |
| 1665 | -------------------------------------- | |
| 1666 | ||
| 1667 | IP version 4 is still the most used protocol in Unix networking. It will be | |
| 1668 | replaced by IP version 6 in the next couple of years, but for the moment it's | |
| 1669 | the de facto standard for the internet and is used in most networking | |
| 1670 | environments around the world. Because of the importance of this protocol, | |
| 1671 | we'll have a deeper look into the subtree controlling the behavior of the IPv4 | |
| 1672 | subsystem of the Linux kernel. | |
| 1673 | ||
| 1674 | Let's start with the entries in /proc/sys/net/ipv4. | |
| 1675 | ||
| 1676 | ICMP settings | |
| 1677 | ------------- | |
| 1678 | ||
| 1679 | icmp_echo_ignore_all and icmp_echo_ignore_broadcasts | |
| 1680 | ---------------------------------------------------- | |
| 1681 | ||
| 1682 | Turn on (1) or off (0), if the kernel should ignore all ICMP ECHO requests, or | |
| 1683 | just those to broadcast and multicast addresses. | |
| 1684 | ||
| 1685 | Please note that if you accept ICMP echo requests with a broadcast/multi\-cast | |
| 1686 | destination address your network may be used as an exploder for denial of | |
| 1687 | service packet flooding attacks to other hosts. | |
| 1688 | ||
| 1689 | icmp_destunreach_rate, icmp_echoreply_rate, icmp_paramprob_rate and icmp_timeexeed_rate | |
| 1690 | --------------------------------------------------------------------------------------- | |
| 1691 | ||
| 1692 | Sets limits for sending ICMP packets to specific targets. A value of zero | |
| 1693 | disables all limiting. Any positive value sets the maximum package rate in | |
| 1694 | hundredth of a second (on Intel systems). | |
| 1695 | ||
| 1696 | IP settings | |
| 1697 | ----------- | |
| 1698 | ||
| 1699 | ip_autoconfig | |
| 1700 | ------------- | |
| 1701 | ||
| 1702 | This file contains the number one if the host received its IP configuration by | |
| 1703 | RARP, BOOTP, DHCP or a similar mechanism. Otherwise it is zero. | |
| 1704 | ||
| 1705 | ip_default_ttl | |
| 1706 | -------------- | |
| 1707 | ||
| 1708 | TTL (Time To Live) for IPv4 interfaces. This is simply the maximum number of | |
| 1709 | hops a packet may travel. | |
| 1710 | ||
| 1711 | ip_dynaddr | |
| 1712 | ---------- | |
| 1713 | ||
| 1714 | Enable dynamic socket address rewriting on interface address change. This is | |
| 1715 | useful for dialup interface with changing IP addresses. | |
| 1716 | ||
| 1717 | ip_forward | |
| 1718 | ---------- | |
| 1719 | ||
| 1720 | Enable or disable forwarding of IP packages between interfaces. Changing this | |
| 1721 | value resets all other parameters to their default values. They differ if the | |
| 1722 | kernel is configured as host or router. | |
| 1723 | ||
| 1724 | ip_local_port_range | |
| 1725 | ------------------- | |
| 1726 | ||
| 1727 | Range of ports used by TCP and UDP to choose the local port. Contains two | |
| 1728 | numbers, the first number is the lowest port, the second number the highest | |
| 1729 | local port. Default is 1024-4999. Should be changed to 32768-61000 for | |
| 1730 | high-usage systems. | |
| 1731 | ||
| 1732 | ip_no_pmtu_disc | |
| 1733 | --------------- | |
| 1734 | ||
| 1735 | Global switch to turn path MTU discovery off. It can also be set on a per | |
| 1736 | socket basis by the applications or on a per route basis. | |
| 1737 | ||
| 1738 | ip_masq_debug | |
| 1739 | ------------- | |
| 1740 | ||
| 1741 | Enable/disable debugging of IP masquerading. | |
| 1742 | ||
| 1743 | IP fragmentation settings | |
| 1744 | ------------------------- | |
| 1745 | ||
| 1746 | ipfrag_high_trash and ipfrag_low_trash | |
| 1747 | -------------------------------------- | |
| 1748 | ||
| 1749 | Maximum memory used to reassemble IP fragments. When ipfrag_high_thresh bytes | |
| 1750 | of memory is allocated for this purpose, the fragment handler will toss | |
| 1751 | packets until ipfrag_low_thresh is reached. | |
| 1752 | ||
| 1753 | ipfrag_time | |
| 1754 | ----------- | |
| 1755 | ||
| 1756 | Time in seconds to keep an IP fragment in memory. | |
| 1757 | ||
| 1758 | TCP settings | |
| 1759 | ------------ | |
| 1760 | ||
| 1761 | tcp_ecn | |
| 1762 | ------- | |
| 1763 | ||
| fa00e7e1 | 1764 | This file controls the use of the ECN bit in the IPv4 headers. This is a new |
| 1da177e4 | 1765 | feature about Explicit Congestion Notification, but some routers and firewalls |
| fa00e7e1 ML |
1766 | block traffic that has this bit set, so it could be necessary to echo 0 to |
| 1767 | /proc/sys/net/ipv4/tcp_ecn if you want to talk to these sites. For more info | |
| 1da177e4 LT |
1768 | you could read RFC2481. |
| 1769 | ||
| 1770 | tcp_retrans_collapse | |
| 1771 | -------------------- | |
| 1772 | ||
| 1773 | Bug-to-bug compatibility with some broken printers. On retransmit, try to send | |
| 1774 | larger packets to work around bugs in certain TCP stacks. Can be turned off by | |
| 1775 | setting it to zero. | |
| 1776 | ||
| 1777 | tcp_keepalive_probes | |
| 1778 | -------------------- | |
| 1779 | ||
| 1780 | Number of keep alive probes TCP sends out, until it decides that the | |
| 1781 | connection is broken. | |
| 1782 | ||
| 1783 | tcp_keepalive_time | |
| 1784 | ------------------ | |
| 1785 | ||
| 1786 | How often TCP sends out keep alive messages, when keep alive is enabled. The | |
| 1787 | default is 2 hours. | |
| 1788 | ||
| 1789 | tcp_syn_retries | |
| 1790 | --------------- | |
| 1791 | ||
| 1792 | Number of times initial SYNs for a TCP connection attempt will be | |
| 1793 | retransmitted. Should not be higher than 255. This is only the timeout for | |
| 1794 | outgoing connections, for incoming connections the number of retransmits is | |
| 1795 | defined by tcp_retries1. | |
| 1796 | ||
| 1797 | tcp_sack | |
| 1798 | -------- | |
| 1799 | ||
| 1800 | Enable select acknowledgments after RFC2018. | |
| 1801 | ||
| 1802 | tcp_timestamps | |
| 1803 | -------------- | |
| 1804 | ||
| 1805 | Enable timestamps as defined in RFC1323. | |
| 1806 | ||
| 1807 | tcp_stdurg | |
| 1808 | ---------- | |
| 1809 | ||
| 1810 | Enable the strict RFC793 interpretation of the TCP urgent pointer field. The | |
| 1811 | default is to use the BSD compatible interpretation of the urgent pointer | |
| 1812 | pointing to the first byte after the urgent data. The RFC793 interpretation is | |
| 1813 | to have it point to the last byte of urgent data. Enabling this option may | |
| 2fe0ae78 | 1814 | lead to interoperability problems. Disabled by default. |
| 1da177e4 LT |
1815 | |
| 1816 | tcp_syncookies | |
| 1817 | -------------- | |
| 1818 | ||
| 1819 | Only valid when the kernel was compiled with CONFIG_SYNCOOKIES. Send out | |
| 1820 | syncookies when the syn backlog queue of a socket overflows. This is to ward | |
| 1821 | off the common 'syn flood attack'. Disabled by default. | |
| 1822 | ||
| 1823 | Note that the concept of a socket backlog is abandoned. This means the peer | |
| 1824 | may not receive reliable error messages from an over loaded server with | |
| 1825 | syncookies enabled. | |
| 1826 | ||
| 1827 | tcp_window_scaling | |
| 1828 | ------------------ | |
| 1829 | ||
| 1830 | Enable window scaling as defined in RFC1323. | |
| 1831 | ||
| 1832 | tcp_fin_timeout | |
| 1833 | --------------- | |
| 1834 | ||
| 1835 | The length of time in seconds it takes to receive a final FIN before the | |
| 1836 | socket is always closed. This is strictly a violation of the TCP | |
| 1837 | specification, but required to prevent denial-of-service attacks. | |
| 1838 | ||
| 1839 | tcp_max_ka_probes | |
| 1840 | ----------------- | |
| 1841 | ||
| 1842 | Indicates how many keep alive probes are sent per slow timer run. Should not | |
| 1843 | be set too high to prevent bursts. | |
| 1844 | ||
| 1845 | tcp_max_syn_backlog | |
| 1846 | ------------------- | |
| 1847 | ||
| 1848 | Length of the per socket backlog queue. Since Linux 2.2 the backlog specified | |
| 1849 | in listen(2) only specifies the length of the backlog queue of already | |
| 1850 | established sockets. When more connection requests arrive Linux starts to drop | |
| 1851 | packets. When syncookies are enabled the packets are still answered and the | |
| 1852 | maximum queue is effectively ignored. | |
| 1853 | ||
| 1854 | tcp_retries1 | |
| 1855 | ------------ | |
| 1856 | ||
| 1857 | Defines how often an answer to a TCP connection request is retransmitted | |
| 1858 | before giving up. | |
| 1859 | ||
| 1860 | tcp_retries2 | |
| 1861 | ------------ | |
| 1862 | ||
| 1863 | Defines how often a TCP packet is retransmitted before giving up. | |
| 1864 | ||
| 1865 | Interface specific settings | |
| 1866 | --------------------------- | |
| 1867 | ||
| 1868 | In the directory /proc/sys/net/ipv4/conf you'll find one subdirectory for each | |
| 1869 | interface the system knows about and one directory calls all. Changes in the | |
| 1870 | all subdirectory affect all interfaces, whereas changes in the other | |
| 1871 | subdirectories affect only one interface. All directories have the same | |
| 1872 | entries: | |
| 1873 | ||
| 1874 | accept_redirects | |
| 1875 | ---------------- | |
| 1876 | ||
| 1877 | This switch decides if the kernel accepts ICMP redirect messages or not. The | |
| 1878 | default is 'yes' if the kernel is configured for a regular host and 'no' for a | |
| 1879 | router configuration. | |
| 1880 | ||
| 1881 | accept_source_route | |
| 1882 | ------------------- | |
| 1883 | ||
| 1884 | Should source routed packages be accepted or declined. The default is | |
| 1885 | dependent on the kernel configuration. It's 'yes' for routers and 'no' for | |
| 1886 | hosts. | |
| 1887 | ||
| 1888 | bootp_relay | |
| 1889 | ~~~~~~~~~~~ | |
| 1890 | ||
| 1891 | Accept packets with source address 0.b.c.d with destinations not to this host | |
| 1892 | as local ones. It is supposed that a BOOTP relay daemon will catch and forward | |
| 1893 | such packets. | |
| 1894 | ||
| 1895 | The default is 0, since this feature is not implemented yet (kernel version | |
| 1896 | 2.2.12). | |
| 1897 | ||
| 1898 | forwarding | |
| 1899 | ---------- | |
| 1900 | ||
| 1901 | Enable or disable IP forwarding on this interface. | |
| 1902 | ||
| 1903 | log_martians | |
| 1904 | ------------ | |
| 1905 | ||
| 1906 | Log packets with source addresses with no known route to kernel log. | |
| 1907 | ||
| 1908 | mc_forwarding | |
| 1909 | ------------- | |
| 1910 | ||
| 1911 | Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE and a | |
| 1912 | multicast routing daemon is required. | |
| 1913 | ||
| 1914 | proxy_arp | |
| 1915 | --------- | |
| 1916 | ||
| 1917 | Does (1) or does not (0) perform proxy ARP. | |
| 1918 | ||
| 1919 | rp_filter | |
| 1920 | --------- | |
| 1921 | ||
| 1922 | Integer value determines if a source validation should be made. 1 means yes, 0 | |
| 1923 | means no. Disabled by default, but local/broadcast address spoofing is always | |
| 1924 | on. | |
| 1925 | ||
| 1926 | If you set this to 1 on a router that is the only connection for a network to | |
| 1927 | the net, it will prevent spoofing attacks against your internal networks | |
| 1928 | (external addresses can still be spoofed), without the need for additional | |
| 1929 | firewall rules. | |
| 1930 | ||
| 1931 | secure_redirects | |
| 1932 | ---------------- | |
| 1933 | ||
| 1934 | Accept ICMP redirect messages only for gateways, listed in default gateway | |
| 1935 | list. Enabled by default. | |
| 1936 | ||
| 1937 | shared_media | |
| 1938 | ------------ | |
| 1939 | ||
| 1940 | If it is not set the kernel does not assume that different subnets on this | |
| 1941 | device can communicate directly. Default setting is 'yes'. | |
| 1942 | ||
| 1943 | send_redirects | |
| 1944 | -------------- | |
| 1945 | ||
| 1946 | Determines whether to send ICMP redirects to other hosts. | |
| 1947 | ||
| 1948 | Routing settings | |
| 1949 | ---------------- | |
| 1950 | ||
| 1951 | The directory /proc/sys/net/ipv4/route contains several file to control | |
| 1952 | routing issues. | |
| 1953 | ||
| 1954 | error_burst and error_cost | |
| 1955 | -------------------------- | |
| 1956 | ||
| 1957 | These parameters are used to limit how many ICMP destination unreachable to | |
| 1958 | send from the host in question. ICMP destination unreachable messages are | |
| 84eb8d06 | 1959 | sent when we cannot reach the next hop while trying to transmit a packet. |
| 1da177e4 LT |
1960 | It will also print some error messages to kernel logs if someone is ignoring |
| 1961 | our ICMP redirects. The higher the error_cost factor is, the fewer | |
| 1962 | destination unreachable and error messages will be let through. Error_burst | |
| 1963 | controls when destination unreachable messages and error messages will be | |
| 1964 | dropped. The default settings limit warning messages to five every second. | |
| 1965 | ||
| 1966 | flush | |
| 1967 | ----- | |
| 1968 | ||
| 1969 | Writing to this file results in a flush of the routing cache. | |
| 1970 | ||
| 1971 | gc_elasticity, gc_interval, gc_min_interval_ms, gc_timeout, gc_thresh | |
| 1972 | --------------------------------------------------------------------- | |
| 1973 | ||
| 1974 | Values to control the frequency and behavior of the garbage collection | |
| 1975 | algorithm for the routing cache. gc_min_interval is deprecated and replaced | |
| 1976 | by gc_min_interval_ms. | |
| 1977 | ||
| 1978 | ||
| 1979 | max_size | |
| 1980 | -------- | |
| 1981 | ||
| 1982 | Maximum size of the routing cache. Old entries will be purged once the cache | |
| 1983 | reached has this size. | |
| 1984 | ||
| 1da177e4 LT |
1985 | redirect_load, redirect_number |
| 1986 | ------------------------------ | |
| 1987 | ||
| 1988 | Factors which determine if more ICPM redirects should be sent to a specific | |
| 1989 | host. No redirects will be sent once the load limit or the maximum number of | |
| 1990 | redirects has been reached. | |
| 1991 | ||
| 1992 | redirect_silence | |
| 1993 | ---------------- | |
| 1994 | ||
| 1995 | Timeout for redirects. After this period redirects will be sent again, even if | |
| 1996 | this has been stopped, because the load or number limit has been reached. | |
| 1997 | ||
| 1998 | Network Neighbor handling | |
| 1999 | ------------------------- | |
| 2000 | ||
| 2001 | Settings about how to handle connections with direct neighbors (nodes attached | |
| 2002 | to the same link) can be found in the directory /proc/sys/net/ipv4/neigh. | |
| 2003 | ||
| 2004 | As we saw it in the conf directory, there is a default subdirectory which | |
| 2005 | holds the default values, and one directory for each interface. The contents | |
| 2006 | of the directories are identical, with the single exception that the default | |
| 2007 | settings contain additional options to set garbage collection parameters. | |
| 2008 | ||
| 2009 | In the interface directories you'll find the following entries: | |
| 2010 | ||
| 2011 | base_reachable_time, base_reachable_time_ms | |
| 2012 | ------------------------------------------- | |
| 2013 | ||
| 2014 | A base value used for computing the random reachable time value as specified | |
| 2015 | in RFC2461. | |
| 2016 | ||
| 2017 | Expression of base_reachable_time, which is deprecated, is in seconds. | |
| 2018 | Expression of base_reachable_time_ms is in milliseconds. | |
| 2019 | ||
| 2020 | retrans_time, retrans_time_ms | |
| 2021 | ----------------------------- | |
| 2022 | ||
| 2023 | The time between retransmitted Neighbor Solicitation messages. | |
| 2024 | Used for address resolution and to determine if a neighbor is | |
| 2025 | unreachable. | |
| 2026 | ||
| 2027 | Expression of retrans_time, which is deprecated, is in 1/100 seconds (for | |
| 2028 | IPv4) or in jiffies (for IPv6). | |
| 2029 | Expression of retrans_time_ms is in milliseconds. | |
| 2030 | ||
| 2031 | unres_qlen | |
| 2032 | ---------- | |
| 2033 | ||
| 2034 | Maximum queue length for a pending arp request - the number of packets which | |
| 2035 | are accepted from other layers while the ARP address is still resolved. | |
| 2036 | ||
| 2037 | anycast_delay | |
| 2038 | ------------- | |
| 2039 | ||
| 2040 | Maximum for random delay of answers to neighbor solicitation messages in | |
| 2041 | jiffies (1/100 sec). Not yet implemented (Linux does not have anycast support | |
| 2042 | yet). | |
| 2043 | ||
| 2044 | ucast_solicit | |
| 2045 | ------------- | |
| 2046 | ||
| 2047 | Maximum number of retries for unicast solicitation. | |
| 2048 | ||
| 2049 | mcast_solicit | |
| 2050 | ------------- | |
| 2051 | ||
| 2052 | Maximum number of retries for multicast solicitation. | |
| 2053 | ||
| 2054 | delay_first_probe_time | |
| 2055 | ---------------------- | |
| 2056 | ||
| 2057 | Delay for the first time probe if the neighbor is reachable. (see | |
| 2058 | gc_stale_time) | |
| 2059 | ||
| 2060 | locktime | |
| 2061 | -------- | |
| 2062 | ||
| 2063 | An ARP/neighbor entry is only replaced with a new one if the old is at least | |
| 2064 | locktime old. This prevents ARP cache thrashing. | |
| 2065 | ||
| 2066 | proxy_delay | |
| 2067 | ----------- | |
| 2068 | ||
| 2069 | Maximum time (real time is random [0..proxytime]) before answering to an ARP | |
| 2070 | request for which we have an proxy ARP entry. In some cases, this is used to | |
| 2071 | prevent network flooding. | |
| 2072 | ||
| 2073 | proxy_qlen | |
| 2074 | ---------- | |
| 2075 | ||
| 2076 | Maximum queue length of the delayed proxy arp timer. (see proxy_delay). | |
| 2077 | ||
| 53cb4726 | 2078 | app_solicit |
| 1da177e4 LT |
2079 | ---------- |
| 2080 | ||
| 2081 | Determines the number of requests to send to the user level ARP daemon. Use 0 | |
| 2082 | to turn off. | |
| 2083 | ||
| 2084 | gc_stale_time | |
| 2085 | ------------- | |
| 2086 | ||
| 2087 | Determines how often to check for stale ARP entries. After an ARP entry is | |
| 2088 | stale it will be resolved again (which is useful when an IP address migrates | |
| 2089 | to another machine). When ucast_solicit is greater than 0 it first tries to | |
| 2090 | send an ARP packet directly to the known host When that fails and | |
| 2091 | mcast_solicit is greater than 0, an ARP request is broadcasted. | |
| 2092 | ||
| 2093 | 2.9 Appletalk | |
| 2094 | ------------- | |
| 2095 | ||
| 2096 | The /proc/sys/net/appletalk directory holds the Appletalk configuration data | |
| 2097 | when Appletalk is loaded. The configurable parameters are: | |
| 2098 | ||
| 2099 | aarp-expiry-time | |
| 2100 | ---------------- | |
| 2101 | ||
| 2102 | The amount of time we keep an ARP entry before expiring it. Used to age out | |
| 2103 | old hosts. | |
| 2104 | ||
| 2105 | aarp-resolve-time | |
| 2106 | ----------------- | |
| 2107 | ||
| 2108 | The amount of time we will spend trying to resolve an Appletalk address. | |
| 2109 | ||
| 2110 | aarp-retransmit-limit | |
| 2111 | --------------------- | |
| 2112 | ||
| 2113 | The number of times we will retransmit a query before giving up. | |
| 2114 | ||
| 2115 | aarp-tick-time | |
| 2116 | -------------- | |
| 2117 | ||
| 2118 | Controls the rate at which expires are checked. | |
| 2119 | ||
| 2120 | The directory /proc/net/appletalk holds the list of active Appletalk sockets | |
| 2121 | on a machine. | |
| 2122 | ||
| 2123 | The fields indicate the DDP type, the local address (in network:node format) | |
| 2124 | the remote address, the size of the transmit pending queue, the size of the | |
| 2125 | received queue (bytes waiting for applications to read) the state and the uid | |
| 2126 | owning the socket. | |
| 2127 | ||
| 2128 | /proc/net/atalk_iface lists all the interfaces configured for appletalk.It | |
| 2129 | shows the name of the interface, its Appletalk address, the network range on | |
| 2130 | that address (or network number for phase 1 networks), and the status of the | |
| 2131 | interface. | |
| 2132 | ||
| 2133 | /proc/net/atalk_route lists each known network route. It lists the target | |
| 2134 | (network) that the route leads to, the router (may be directly connected), the | |
| 2135 | route flags, and the device the route is using. | |
| 2136 | ||
| 2137 | 2.10 IPX | |
| 2138 | -------- | |
| 2139 | ||
| 2140 | The IPX protocol has no tunable values in proc/sys/net. | |
| 2141 | ||
| 2142 | The IPX protocol does, however, provide proc/net/ipx. This lists each IPX | |
| 2143 | socket giving the local and remote addresses in Novell format (that is | |
| 2144 | network:node:port). In accordance with the strange Novell tradition, | |
| 2145 | everything but the port is in hex. Not_Connected is displayed for sockets that | |
| 2146 | are not tied to a specific remote address. The Tx and Rx queue sizes indicate | |
| 2147 | the number of bytes pending for transmission and reception. The state | |
| 2148 | indicates the state the socket is in and the uid is the owning uid of the | |
| 2149 | socket. | |
| 2150 | ||
| 2151 | The /proc/net/ipx_interface file lists all IPX interfaces. For each interface | |
| 2152 | it gives the network number, the node number, and indicates if the network is | |
| 2153 | the primary network. It also indicates which device it is bound to (or | |
| 2154 | Internal for internal networks) and the Frame Type if appropriate. Linux | |
| 2155 | supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet framing for | |
| 2156 | IPX. | |
| 2157 | ||
| 2158 | The /proc/net/ipx_route table holds a list of IPX routes. For each route it | |
| 2159 | gives the destination network, the router node (or Directly) and the network | |
| 2160 | address of the router (or Connected) for internal networks. | |
| 2161 | ||
| 2162 | 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem | |
| 2163 | ---------------------------------------------------------- | |
| 2164 | ||
| 2165 | The "mqueue" filesystem provides the necessary kernel features to enable the | |
| 2166 | creation of a user space library that implements the POSIX message queues | |
| 2167 | API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System | |
| 2168 | Interfaces specification.) | |
| 2169 | ||
| 2170 | The "mqueue" filesystem contains values for determining/setting the amount of | |
| 2171 | resources used by the file system. | |
| 2172 | ||
| 2173 | /proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the | |
| 2174 | maximum number of message queues allowed on the system. | |
| 2175 | ||
| 2176 | /proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the | |
| 2177 | maximum number of messages in a queue value. In fact it is the limiting value | |
| 2178 | for another (user) limit which is set in mq_open invocation. This attribute of | |
| 2179 | a queue must be less or equal then msg_max. | |
| 2180 | ||
| 2181 | /proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the | |
| 2182 | maximum message size value (it is every message queue's attribute set during | |
| 2183 | its creation). | |
| 2184 | ||
| d7ff0dbf JFM |
2185 | 2.12 /proc/<pid>/oom_adj - Adjust the oom-killer score |
| 2186 | ------------------------------------------------------ | |
| 2187 | ||
| 2188 | This file can be used to adjust the score used to select which processes | |
| 2189 | should be killed in an out-of-memory situation. Giving it a high score will | |
| 2190 | increase the likelihood of this process being killed by the oom-killer. Valid | |
| 2191 | values are in the range -16 to +15, plus the special value -17, which disables | |
| 2192 | oom-killing altogether for this process. | |
| 2193 | ||
| 2194 | 2.13 /proc/<pid>/oom_score - Display current oom-killer score | |
| 2195 | ------------------------------------------------------------- | |
| 2196 | ||
| 2197 | ------------------------------------------------------------------------------ | |
| 2198 | This file can be used to check the current score used by the oom-killer is for | |
| 2199 | any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which | |
| 2200 | process should be killed in an out-of-memory situation. | |
| 1da177e4 LT |
2201 | |
| 2202 | ------------------------------------------------------------------------------ | |
| 2203 | Summary | |
| 2204 | ------------------------------------------------------------------------------ | |
| 2205 | Certain aspects of kernel behavior can be modified at runtime, without the | |
| 2206 | need to recompile the kernel, or even to reboot the system. The files in the | |
| 2207 | /proc/sys tree can not only be read, but also modified. You can use the echo | |
| 2208 | command to write value into these files, thereby changing the default settings | |
| 2209 | of the kernel. | |
| 2210 | ------------------------------------------------------------------------------ | |
| f9c99463 RK |
2211 | |
| 2212 | 2.14 /proc/<pid>/io - Display the IO accounting fields | |
| 2213 | ------------------------------------------------------- | |
| 2214 | ||
| 2215 | This file contains IO statistics for each running process | |
| 2216 | ||
| 2217 | Example | |
| 2218 | ------- | |
| 2219 | ||
| 2220 | test:/tmp # dd if=/dev/zero of=/tmp/test.dat & | |
| 2221 | [1] 3828 | |
| 2222 | ||
| 2223 | test:/tmp # cat /proc/3828/io | |
| 2224 | rchar: 323934931 | |
| 2225 | wchar: 323929600 | |
| 2226 | syscr: 632687 | |
| 2227 | syscw: 632675 | |
| 2228 | read_bytes: 0 | |
| 2229 | write_bytes: 323932160 | |
| 2230 | cancelled_write_bytes: 0 | |
| 2231 | ||
| 2232 | ||
| 2233 | Description | |
| 2234 | ----------- | |
| 2235 | ||
| 2236 | rchar | |
| 2237 | ----- | |
| 2238 | ||
| 2239 | I/O counter: chars read | |
| 2240 | The number of bytes which this task has caused to be read from storage. This | |
| 2241 | is simply the sum of bytes which this process passed to read() and pread(). | |
| 2242 | It includes things like tty IO and it is unaffected by whether or not actual | |
| 2243 | physical disk IO was required (the read might have been satisfied from | |
| 2244 | pagecache) | |
| 2245 | ||
| 2246 | ||
| 2247 | wchar | |
| 2248 | ----- | |
| 2249 | ||
| 2250 | I/O counter: chars written | |
| 2251 | The number of bytes which this task has caused, or shall cause to be written | |
| 2252 | to disk. Similar caveats apply here as with rchar. | |
| 2253 | ||
| 2254 | ||
| 2255 | syscr | |
| 2256 | ----- | |
| 2257 | ||
| 2258 | I/O counter: read syscalls | |
| 2259 | Attempt to count the number of read I/O operations, i.e. syscalls like read() | |
| 2260 | and pread(). | |
| 2261 | ||
| 2262 | ||
| 2263 | syscw | |
| 2264 | ----- | |
| 2265 | ||
| 2266 | I/O counter: write syscalls | |
| 2267 | Attempt to count the number of write I/O operations, i.e. syscalls like | |
| 2268 | write() and pwrite(). | |
| 2269 | ||
| 2270 | ||
| 2271 | read_bytes | |
| 2272 | ---------- | |
| 2273 | ||
| 2274 | I/O counter: bytes read | |
| 2275 | Attempt to count the number of bytes which this process really did cause to | |
| 2276 | be fetched from the storage layer. Done at the submit_bio() level, so it is | |
| 2277 | accurate for block-backed filesystems. <please add status regarding NFS and | |
| 2278 | CIFS at a later time> | |
| 2279 | ||
| 2280 | ||
| 2281 | write_bytes | |
| 2282 | ----------- | |
| 2283 | ||
| 2284 | I/O counter: bytes written | |
| 2285 | Attempt to count the number of bytes which this process caused to be sent to | |
| 2286 | the storage layer. This is done at page-dirtying time. | |
| 2287 | ||
| 2288 | ||
| 2289 | cancelled_write_bytes | |
| 2290 | --------------------- | |
| 2291 | ||
| 2292 | The big inaccuracy here is truncate. If a process writes 1MB to a file and | |
| 2293 | then deletes the file, it will in fact perform no writeout. But it will have | |
| 2294 | been accounted as having caused 1MB of write. | |
| 2295 | In other words: The number of bytes which this process caused to not happen, | |
| 2296 | by truncating pagecache. A task can cause "negative" IO too. If this task | |
| 2297 | truncates some dirty pagecache, some IO which another task has been accounted | |
| 2298 | for (in it's write_bytes) will not be happening. We _could_ just subtract that | |
| 2299 | from the truncating task's write_bytes, but there is information loss in doing | |
| 2300 | that. | |
| 2301 | ||
| 2302 | ||
| 2303 | Note | |
| 2304 | ---- | |
| 2305 | ||
| 2306 | At its current implementation state, this is a bit racy on 32-bit machines: if | |
| 2307 | process A reads process B's /proc/pid/io while process B is updating one of | |
| 2308 | those 64-bit counters, process A could see an intermediate result. | |
| 2309 | ||
| 2310 | ||
| 2311 | More information about this can be found within the taskstats documentation in | |
| 2312 | Documentation/accounting. | |
| 2313 | ||
| bb90110d KH |
2314 | 2.15 /proc/<pid>/coredump_filter - Core dump filtering settings |
| 2315 | --------------------------------------------------------------- | |
| 2316 | When a process is dumped, all anonymous memory is written to a core file as | |
| 2317 | long as the size of the core file isn't limited. But sometimes we don't want | |
| 2318 | to dump some memory segments, for example, huge shared memory. Conversely, | |
| 2319 | sometimes we want to save file-backed memory segments into a core file, not | |
| 2320 | only the individual files. | |
| 2321 | ||
| 2322 | /proc/<pid>/coredump_filter allows you to customize which memory segments | |
| 2323 | will be dumped when the <pid> process is dumped. coredump_filter is a bitmask | |
| 2324 | of memory types. If a bit of the bitmask is set, memory segments of the | |
| 2325 | corresponding memory type are dumped, otherwise they are not dumped. | |
| 2326 | ||
| 2327 | The following 4 memory types are supported: | |
| 2328 | - (bit 0) anonymous private memory | |
| 2329 | - (bit 1) anonymous shared memory | |
| 2330 | - (bit 2) file-backed private memory | |
| 2331 | - (bit 3) file-backed shared memory | |
| 2332 | ||
| 2333 | Note that MMIO pages such as frame buffer are never dumped and vDSO pages | |
| 2334 | are always dumped regardless of the bitmask status. | |
| 2335 | ||
| 2336 | Default value of coredump_filter is 0x3; this means all anonymous memory | |
| 2337 | segments are dumped. | |
| 2338 | ||
| 2339 | If you don't want to dump all shared memory segments attached to pid 1234, | |
| 2340 | write 1 to the process's proc file. | |
| 2341 | ||
| 2342 | $ echo 0x1 > /proc/1234/coredump_filter | |
| 2343 | ||
| 2344 | When a new process is created, the process inherits the bitmask status from its | |
| 2345 | parent. It is useful to set up coredump_filter before the program runs. | |
| 2346 | For example: | |
| 2347 | ||
| 2348 | $ echo 0x7 > /proc/self/coredump_filter | |
| 2349 | $ ./some_program | |
| 2350 | ||
| f9c99463 | 2351 | ------------------------------------------------------------------------------ |