------------------------------------------------------------------------------ T H E /proc F I L E S Y S T E M ------------------------------------------------------------------------------ /proc/sys Terrehon Bowden October 7 1999 Bodo Bauer 2.4.x update Jorge Nerin November 14 2000 move /proc/sys Shen Feng April 1 2009 ------------------------------------------------------------------------------ Version 1.3 Kernel version 2.2.12 Kernel version 2.4.0-test11-pre4 ------------------------------------------------------------------------------ fixes/update part 1.1 Stefani Seibold June 9 2009 Table of Contents ----------------- 0 Preface 0.1 Introduction/Credits 0.2 Legal Stuff 1 Collecting System Information 1.1 Process-Specific Subdirectories 1.2 Kernel data 1.3 IDE devices in /proc/ide 1.4 Networking info in /proc/net 1.5 SCSI info 1.6 Parallel port info in /proc/parport 1.7 TTY info in /proc/tty 1.8 Miscellaneous kernel statistics in /proc/stat 1.9 Ext4 file system parameters 2 Modifying System Parameters 3 Per-Process Parameters 3.1 /proc//oom_score_adj - Adjust the oom-killer score 3.2 /proc//oom_score - Display current oom-killer score 3.3 /proc//io - Display the IO accounting fields 3.4 /proc//coredump_filter - Core dump filtering settings 3.5 /proc//mountinfo - Information about mounts 3.6 /proc//comm & /proc//task//comm 3.7 /proc//task//children - Information about task children 4 Configuring procfs 4.1 Mount options ------------------------------------------------------------------------------ Preface ------------------------------------------------------------------------------ 0.1 Introduction/Credits ------------------------ This documentation is part of a soon (or so we hope) to be released book on the SuSE Linux distribution. As there is no complete documentation for the /proc file system and we've used many freely available sources to write these chapters, it seems only fair to give the work back to the Linux community. This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm afraid it's still far from complete, but we hope it will be useful. As far as we know, it is the first 'all-in-one' document about the /proc file system. It is focused on the Intel x86 hardware, so if you are looking for PPC, ARM, SPARC, AXP, etc., features, you probably won't find what you are looking for. It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But additions and patches are welcome and will be added to this document if you mail them to Bodo. We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of other people for help compiling this documentation. We'd also like to extend a special thank you to Andi Kleen for documentation, which we relied on heavily to create this document, as well as the additional information he provided. Thanks to everybody else who contributed source or docs to the Linux kernel and helped create a great piece of software... :) If you have any comments, corrections or additions, please don't hesitate to contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this document. The latest version of this document is available online at http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html If the above direction does not works for you, you could try the kernel mailing list at linux-kernel@vger.kernel.org and/or try to reach me at comandante@zaralinux.com. 0.2 Legal Stuff --------------- We don't guarantee the correctness of this document, and if you come to us complaining about how you screwed up your system because of incorrect documentation, we won't feel responsible... ------------------------------------------------------------------------------ CHAPTER 1: COLLECTING SYSTEM INFORMATION ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ In This Chapter ------------------------------------------------------------------------------ * Investigating the properties of the pseudo file system /proc and its ability to provide information on the running Linux system * Examining /proc's structure * Uncovering various information about the kernel and the processes running on the system ------------------------------------------------------------------------------ The proc file system acts as an interface to internal data structures in the kernel. It can be used to obtain information about the system and to change certain kernel parameters at runtime (sysctl). First, we'll take a look at the read-only parts of /proc. In Chapter 2, we show you how you can use /proc/sys to change settings. 1.1 Process-Specific Subdirectories ----------------------------------- The directory /proc contains (among other things) one subdirectory for each process running on the system, which is named after the process ID (PID). The link self points to the process reading the file system. Each process subdirectory has the entries listed in Table 1-1. Table 1-1: Process specific entries in /proc .............................................................................. File Content clear_refs Clears page referenced bits shown in smaps output cmdline Command line arguments cpu Current and last cpu in which it was executed (2.4)(smp) cwd Link to the current working directory environ Values of environment variables exe Link to the executable of this process fd Directory, which contains all file descriptors maps Memory maps to executables and library files (2.4) mem Memory held by this process root Link to the root directory of this process stat Process status statm Process memory status information status Process status in human readable form wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan pagemap Page table stack Report full stack trace, enable via CONFIG_STACKTRACE smaps a extension based on maps, showing the memory consumption of each mapping .............................................................................. For example, to get the status information of a process, all you have to do is read the file /proc/PID/status: >cat /proc/self/status Name: cat State: R (running) Tgid: 5452 Pid: 5452 PPid: 743 TracerPid: 0 (2.4) Uid: 501 501 501 501 Gid: 100 100 100 100 FDSize: 256 Groups: 100 14 16 VmPeak: 5004 kB VmSize: 5004 kB VmLck: 0 kB VmHWM: 476 kB VmRSS: 476 kB VmData: 156 kB VmStk: 88 kB VmExe: 68 kB VmLib: 1412 kB VmPTE: 20 kb VmSwap: 0 kB Threads: 1 SigQ: 0/28578 SigPnd: 0000000000000000 ShdPnd: 0000000000000000 SigBlk: 0000000000000000 SigIgn: 0000000000000000 SigCgt: 0000000000000000 CapInh: 00000000fffffeff CapPrm: 0000000000000000 CapEff: 0000000000000000 CapBnd: ffffffffffffffff voluntary_ctxt_switches: 0 nonvoluntary_ctxt_switches: 1 This shows you nearly the same information you would get if you viewed it with the ps command. In fact, ps uses the proc file system to obtain its information. But you get a more detailed view of the process by reading the file /proc/PID/status. It fields are described in table 1-2. The statm file contains more detailed information about the process memory usage. Its seven fields are explained in Table 1-3. The stat file contains details information about the process itself. Its fields are explained in Table 1-4. (for SMP CONFIG users) For making accounting scalable, RSS related information are handled in asynchronous manner and the vaule may not be very precise. To see a precise snapshot of a moment, you can see /proc//smaps file and scan page table. It's slow but very precise. Table 1-2: Contents of the status files (as of 2.6.30-rc7) .............................................................................. Field Content Name filename of the executable State state (R is running, S is sleeping, D is sleeping in an uninterruptible wait, Z is zombie, T is traced or stopped) Tgid thread group ID Pid process id PPid process id of the parent process TracerPid PID of process tracing this process (0 if not) Uid Real, effective, saved set, and file system UIDs Gid Real, effective, saved set, and file system GIDs FDSize number of file descriptor slots currently allocated Groups supplementary group list VmPeak peak virtual memory size VmSize total program size VmLck locked memory size VmHWM peak resident set size ("high water mark") VmRSS size of memory portions VmData size of data, stack, and text segments VmStk size of data, stack, and text segments VmExe size of text segment VmLib size of shared library code VmPTE size of page table entries VmSwap size of swap usage (the number of referred swapents) Threads number of threads SigQ number of signals queued/max. number for queue SigPnd bitmap of pending signals for the thread ShdPnd bitmap of shared pending signals for the process SigBlk bitmap of blocked signals SigIgn bitmap of ignored signals SigCgt bitmap of catched signals CapInh bitmap of inheritable capabilities CapPrm bitmap of permitted capabilities CapEff bitmap of effective capabilities CapBnd bitmap of capabilities bounding set Cpus_allowed mask of CPUs on which this process may run Cpus_allowed_list Same as previous, but in "list format" Mems_allowed mask of memory nodes allowed to this process Mems_allowed_list Same as previous, but in "list format" voluntary_ctxt_switches number of voluntary context switches nonvoluntary_ctxt_switches number of non voluntary context switches .............................................................................. Table 1-3: Contents of the statm files (as of 2.6.8-rc3) .............................................................................. Field Content size total program size (pages) (same as VmSize in status) resident size of memory portions (pages) (same as VmRSS in status) shared number of pages that are shared (i.e. backed by a file) trs number of pages that are 'code' (not including libs; broken, includes data segment) lrs number of pages of library (always 0 on 2.6) drs number of pages of data/stack (including libs; broken, includes library text) dt number of dirty pages (always 0 on 2.6) .............................................................................. Table 1-4: Contents of the stat files (as of 2.6.30-rc7) .............................................................................. Field Content pid process id tcomm filename of the executable state state (R is running, S is sleeping, D is sleeping in an uninterruptible wait, Z is zombie, T is traced or stopped) ppid process id of the parent process pgrp pgrp of the process sid session id tty_nr tty the process uses tty_pgrp pgrp of the tty flags task flags min_flt number of minor faults cmin_flt number of minor faults with child's maj_flt number of major faults cmaj_flt number of major faults with child's utime user mode jiffies stime kernel mode jiffies cutime user mode jiffies with child's cstime kernel mode jiffies with child's priority priority level nice nice level num_threads number of threads it_real_value (obsolete, always 0) start_time time the process started after system boot vsize virtual memory size rss resident set memory size rsslim current limit in bytes on the rss start_code address above which program text can run end_code address below which program text can run start_stack address of the start of the main process stack esp current value of ESP eip current value of EIP pending bitmap of pending signals blocked bitmap of blocked signals sigign bitmap of ignored signals sigcatch bitmap of catched signals wchan address where process went to sleep 0 (place holder) 0 (place holder) exit_signal signal to send to parent thread on exit task_cpu which CPU the task is scheduled on rt_priority realtime priority policy scheduling policy (man sched_setscheduler) blkio_ticks time spent waiting for block IO gtime guest time of the task in jiffies cgtime guest time of the task children in jiffies start_data address above which program data+bss is placed end_data address below which program data+bss is placed start_brk address above which program heap can be expanded with brk() arg_start address above which program command line is placed arg_end address below which program command line is placed env_start address above which program environment is placed env_end address below which program environment is placed exit_code the thread's exit_code in the form reported by the waitpid system call .............................................................................. The /proc/PID/maps file containing the currently mapped memory regions and their access permissions. The format is: address perms offset dev inode pathname 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test 0804a000-0806b000 rw-p 00000000 00:00 0 [heap] a7cb1000-a7cb2000 ---p 00000000 00:00 0 a7cb2000-a7eb2000 rw-p 00000000 00:00 0 a7eb2000-a7eb3000 ---p 00000000 00:00 0 a7eb3000-a7ed5000 rw-p 00000000 00:00 0 [stack:1001] a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6 a800b000-a800e000 rw-p 00000000 00:00 0 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0 a8024000-a8027000 rw-p 00000000 00:00 0 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack] ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso] where "address" is the address space in the process that it occupies, "perms" is a set of permissions: r = read w = write x = execute s = shared p = private (copy on write) "offset" is the offset into the mapping, "dev" is the device (major:minor), and "inode" is the inode on that device. 0 indicates that no inode is associated with the memory region, as the case would be with BSS (uninitialized data). The "pathname" shows the name associated file for this mapping. If the mapping is not associated with a file: [heap] = the heap of the program [stack] = the stack of the main process [stack:1001] = the stack of the thread with tid 1001 [vdso] = the "virtual dynamic shared object", the kernel system call handler or if empty, the mapping is anonymous. The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint of the individual tasks of a process. In this file you will see a mapping marked as [stack] if that task sees it as a stack. This is a key difference from the content of /proc/PID/maps, where you will see all mappings that are being used as stack by all of those tasks. Hence, for the example above, the task-level map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this: 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test 0804a000-0806b000 rw-p 00000000 00:00 0 [heap] a7cb1000-a7cb2000 ---p 00000000 00:00 0 a7cb2000-a7eb2000 rw-p 00000000 00:00 0 a7eb2000-a7eb3000 ---p 00000000 00:00 0 a7eb3000-a7ed5000 rw-p 00000000 00:00 0 [stack] a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6 a800b000-a800e000 rw-p 00000000 00:00 0 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0 a8024000-a8027000 rw-p 00000000 00:00 0 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2 aff35000-aff4a000 rw-p 00000000 00:00 0 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso] The /proc/PID/smaps is an extension based on maps, showing the memory consumption for each of the process's mappings. For each of mappings there is a series of lines such as the following: 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash Size: 1084 kB Rss: 892 kB Pss: 374 kB Shared_Clean: 892 kB Shared_Dirty: 0 kB Private_Clean: 0 kB Private_Dirty: 0 kB Referenced: 892 kB Anonymous: 0 kB Swap: 0 kB KernelPageSize: 4 kB MMUPageSize: 4 kB Locked: 374 kB The first of these lines shows the same information as is displayed for the mapping in /proc/PID/maps. The remaining lines show the size of the mapping (size), the amount of the mapping that is currently resident in RAM (RSS), the process' proportional share of this mapping (PSS), the number of clean and dirty private pages in the mapping. Note that even a page which is part of a MAP_SHARED mapping, but has only a single pte mapped, i.e. is currently used by only one process, is accounted as private and not as shared. "Referenced" indicates the amount of memory currently marked as referenced or accessed. "Anonymous" shows the amount of memory that does not belong to any file. Even a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE and a page is modified, the file page is replaced by a private anonymous copy. "Swap" shows how much would-be-anonymous memory is also used, but out on swap. This file is only present if the CONFIG_MMU kernel configuration option is enabled. The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG bits on both physical and virtual pages associated with a process. To clear the bits for all the pages associated with the process > echo 1 > /proc/PID/clear_refs To clear the bits for the anonymous pages associated with the process > echo 2 > /proc/PID/clear_refs To clear the bits for the file mapped pages associated with the process > echo 3 > /proc/PID/clear_refs Any other value written to /proc/PID/clear_refs will have no effect. The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags using /proc/kpageflags and number of times a page is mapped using /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt. 1.2 Kernel data --------------- Similar to the process entries, the kernel data files give information about the running kernel. The files used to obtain this information are contained in /proc and are listed in Table 1-5. Not all of these will be present in your system. It depends on the kernel configuration and the loaded modules, which files are there, and which are missing. Table 1-5: Kernel info in /proc .............................................................................. File Content apm Advanced power management info buddyinfo Kernel memory allocator information (see text) (2.5) bus Directory containing bus specific information cmdline Kernel command line cpuinfo Info about the CPU devices Available devices (block and character) dma Used DMS channels filesystems Supported filesystems driver Various drivers grouped here, currently rtc (2.4) execdomains Execdomains, related to security (2.4) fb Frame Buffer devices (2.4) fs File system parameters, currently nfs/exports (2.4) ide Directory containing info about the IDE subsystem interrupts Interrupt usage iomem Memory map (2.4) ioports I/O port usage irq Masks for irq to cpu affinity (2.4)(smp?) isapnp ISA PnP (Plug&Play) Info (2.4) kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4)) kmsg Kernel messages ksyms Kernel symbol table loadavg Load average of last 1, 5 & 15 minutes locks Kernel locks meminfo Memory info misc Miscellaneous modules List of loaded modules mounts Mounted filesystems net Networking info (see text) pagetypeinfo Additional page allocator information (see text) (2.5) partitions Table of partitions known to the system pci Deprecated info of PCI bus (new way -> /proc/bus/pci/, decoupled by lspci (2.4) rtc Real time clock scsi SCSI info (see text) slabinfo Slab pool info softirqs softirq usage stat Overall statistics swaps Swap space utilization sys See chapter 2 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4) tty Info of tty drivers uptime System uptime version Kernel version video bttv info of video resources (2.4) vmallocinfo Show vmalloced areas .............................................................................. You can, for example, check which interrupts are currently in use and what they are used for by looking in the file /proc/interrupts: > cat /proc/interrupts CPU0 0: 8728810 XT-PIC timer 1: 895 XT-PIC keyboard 2: 0 XT-PIC cascade 3: 531695 XT-PIC aha152x 4: 2014133 XT-PIC serial 5: 44401 XT-PIC pcnet_cs 8: 2 XT-PIC rtc 11: 8 XT-PIC i82365 12: 182918 XT-PIC PS/2 Mouse 13: 1 XT-PIC fpu 14: 1232265 XT-PIC ide0 15: 7 XT-PIC ide1 NMI: 0 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the output of a SMP machine): > cat /proc/interrupts CPU0 CPU1 0: 1243498 1214548 IO-APIC-edge timer 1: 8949 8958 IO-APIC-edge keyboard 2: 0 0 XT-PIC cascade 5: 11286 10161 IO-APIC-edge soundblaster 8: 1 0 IO-APIC-edge rtc 9: 27422 27407 IO-APIC-edge 3c503 12: 113645 113873 IO-APIC-edge PS/2 Mouse 13: 0 0 XT-PIC fpu 14: 22491 24012 IO-APIC-edge ide0 15: 2183 2415 IO-APIC-edge ide1 17: 30564 30414 IO-APIC-level eth0 18: 177 164 IO-APIC-level bttv NMI: 2457961 2457959 LOC: 2457882 2457881 ERR: 2155 NMI is incremented in this case because every timer interrupt generates a NMI (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups. LOC is the local interrupt counter of the internal APIC of every CPU. ERR is incremented in the case of errors in the IO-APIC bus (the bus that connects the CPUs in a SMP system. This means that an error has been detected, the IO-APIC automatically retry the transmission, so it should not be a big problem, but you should read the SMP-FAQ. In 2.6.2* /proc/interrupts was expanded again. This time the goal was for /proc/interrupts to display every IRQ vector in use by the system, not just those considered 'most important'. The new vectors are: THR -- interrupt raised when a machine check threshold counter (typically counting ECC corrected errors of memory or cache) exceeds a configurable threshold. Only available on some systems. TRM -- a thermal event interrupt occurs when a temperature threshold has been exceeded for the CPU. This interrupt may also be generated when the temperature drops back to normal. SPU -- a spurious interrupt is some interrupt that was raised then lowered by some IO device before it could be fully processed by the APIC. Hence the APIC sees the interrupt but does not know what device it came from. For this case the APIC will generate the interrupt with a IRQ vector of 0xff. This might also be generated by chipset bugs. RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are sent from one CPU to another per the needs of the OS. Typically, their statistics are used by kernel developers and interested users to determine the occurrence of interrupts of the given type. The above IRQ vectors are displayed only when relevant. For example, the threshold vector does not exist on x86_64 platforms. Others are suppressed when the system is a uniprocessor. As of this writing, only i386 and x86_64 platforms support the new IRQ vector displays. Of some interest is the introduction of the /proc/irq directory to 2.4. It could be used to set IRQ to CPU affinity, this means that you can "hook" an IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and prof_cpu_mask. For example > ls /proc/irq/ 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask 1 11 13 15 17 19 3 5 7 9 default_smp_affinity > ls /proc/irq/0/ smp_affinity smp_affinity is a bitmask, in which you can specify which CPUs can handle the IRQ, you can set it by doing: > echo 1 > /proc/irq/10/smp_affinity This means that only the first CPU will handle the IRQ, but you can also echo 5 which means that only the first and fourth CPU can handle the IRQ. The contents of each smp_affinity file is the same by default: > cat /proc/irq/0/smp_affinity ffffffff There is an alternate interface, smp_affinity_list which allows specifying a cpu range instead of a bitmask: > cat /proc/irq/0/smp_affinity_list 1024-1031 The default_smp_affinity mask applies to all non-active IRQs, which are the IRQs which have not yet been allocated/activated, and hence which lack a /proc/irq/[0-9]* directory. The node file on an SMP system shows the node to which the device using the IRQ reports itself as being attached. This hardware locality information does not include information about any possible driver locality preference. prof_cpu_mask specifies which CPUs are to be profiled by the system wide profiler. Default value is ffffffff (all cpus if there are only 32 of them). The way IRQs are routed is handled by the IO-APIC, and it's Round Robin between all the CPUs which are allowed to handle it. As usual the kernel has more info than you and does a better job than you, so the defaults are the best choice for almost everyone. [Note this applies only to those IO-APIC's that support "Round Robin" interrupt distribution.] There are three more important subdirectories in /proc: net, scsi, and sys. The general rule is that the contents, or even the existence of these directories, depend on your kernel configuration. If SCSI is not enabled, the directory scsi may not exist. The same is true with the net, which is there only when networking support is present in the running kernel. The slabinfo file gives information about memory usage at the slab level. Linux uses slab pools for memory management above page level in version 2.2. Commonly used objects have their own slab pool (such as network buffers, directory cache, and so on). .............................................................................. > cat /proc/buddyinfo Node 0, zone DMA 0 4 5 4 4 3 ... Node 0, zone Normal 1 0 0 1 101 8 ... Node 0, zone HighMem 2 0 0 1 1 0 ... External fragmentation is a problem under some workloads, and buddyinfo is a useful tool for helping diagnose these problems. Buddyinfo will give you a clue as to how big an area you can safely allocate, or why a previous allocation failed. Each column represents the number of pages of a certain order which are available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE available in ZONE_NORMAL, etc... More information relevant to external fragmentation can be found in pagetypeinfo. > cat /proc/pagetypeinfo Page block order: 9 Pages per block: 512 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate Node 0, zone DMA 2 0 5 1 0 Node 0, zone DMA32 41 6 967 2 0 Fragmentation avoidance in the kernel works by grouping pages of different migrate types into the same contiguous regions of memory called page blocks. A page block is typically the size of the default hugepage size e.g. 2MB on X86-64. By keeping pages grouped based on their ability to move, the kernel can reclaim pages within a page block to satisfy a high-order allocation. The pagetypinfo begins with information on the size of a page block. It then gives the same type of information as buddyinfo except broken down by migrate-type and finishes with details on how many page blocks of each type exist. If min_free_kbytes has been tuned correctly (recommendations made by hugeadm from libhugetlbfs http://sourceforge.net/projects/libhugetlbfs/), one can make an estimate of the likely number of huge pages that can be allocated at a given point in time. All the "Movable" blocks should be allocatable unless memory has been mlock()'d. Some of the Reclaimable blocks should also be allocatable although a lot of filesystem metadata may have to be reclaimed to achieve this. .............................................................................. meminfo: Provides information about distribution and utilization of memory. This varies by architecture and compile options. The following is from a 16GB PIII, which has highmem enabled. You may not have all of these fields. > cat /proc/meminfo The "Locked" indicates whether the mapping is locked in memory or not. MemTotal: 16344972 kB MemFree: 13634064 kB Buffers: 3656 kB Cached: 1195708 kB SwapCached: 0 kB Active: 891636 kB Inactive: 1077224 kB HighTotal: 15597528 kB HighFree: 13629632 kB LowTotal: 747444 kB LowFree: 4432 kB SwapTotal: 0 kB SwapFree: 0 kB Dirty: 968 kB Writeback: 0 kB AnonPages: 861800 kB Mapped: 280372 kB Slab: 284364 kB SReclaimable: 159856 kB SUnreclaim: 124508 kB PageTables: 24448 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 7669796 kB Committed_AS: 100056 kB VmallocTotal: 112216 kB VmallocUsed: 428 kB VmallocChunk: 111088 kB AnonHugePages: 49152 kB MemTotal: Total usable ram (i.e. physical ram minus a few reserved bits and the kernel binary code) MemFree: The sum of LowFree+HighFree Buffers: Relatively temporary storage for raw disk blocks shouldn't get tremendously large (20MB or so) Cached: in-memory cache for files read from the disk (the pagecache). Doesn't include SwapCached SwapCached: Memory that once was swapped out, is swapped back in but still also is in the swapfile (if memory is needed it doesn't need to be swapped out AGAIN because it is already in the swapfile. This saves I/O) Active: Memory that has been used more recently and usually not reclaimed unless absolutely necessary. Inactive: Memory which has been less recently used. It is more eligible to be reclaimed for other purposes HighTotal: HighFree: Highmem is all memory above ~860MB of physical memory Highmem areas are for use by userspace programs, or for the pagecache. The kernel must use tricks to access this memory, making it slower to access than lowmem. LowTotal: LowFree: Lowmem is memory which can be used for everything that highmem can be used for, but it is also available for the kernel's use for its own data structures. Among many other things, it is where everything from the Slab is allocated. Bad things happen when you're out of lowmem. SwapTotal: total amount of swap space available SwapFree: Memory which has been evicted from RAM, and is temporarily on the disk Dirty: Memory which is waiting to get written back to the disk Writeback: Memory which is actively being written back to the disk AnonPages: Non-file backed pages mapped into userspace page tables AnonHugePages: Non-file backed huge pages mapped into userspace page tables Mapped: files which have been mmaped, such as libraries Slab: in-kernel data structures cache SReclaimable: Part of Slab, that might be reclaimed, such as caches SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure PageTables: amount of memory dedicated to the lowest level of page tables. NFS_Unstable: NFS pages sent to the server, but not yet committed to stable storage Bounce: Memory used for block device "bounce buffers" WritebackTmp: Memory used by FUSE for temporary writeback buffers CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'), this is the total amount of memory currently available to be allocated on the system. This limit is only adhered to if strict overcommit accounting is enabled (mode 2 in 'vm.overcommit_memory'). The CommitLimit is calculated with the following formula: CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap For example, on a system with 1G of physical RAM and 7G of swap with a `vm.overcommit_ratio` of 30 it would yield a CommitLimit of 7.3G. For more details, see the memory overcommit documentation in vm/overcommit-accounting. Committed_AS: The amount of memory presently allocated on the system. The committed memory is a sum of all of the memory which has been allocated by processes, even if it has not been "used" by them as of yet. A process which malloc()'s 1G of memory, but only touches 300M of it will only show up as using 300M of memory even if it has the address space allocated for the entire 1G. This 1G is memory which has been "committed" to by the VM and can be used at any time by the allocating application. With strict overcommit enabled on the system (mode 2 in 'vm.overcommit_memory'), allocations which would exceed the CommitLimit (detailed above) will not be permitted. This is useful if one needs to guarantee that processes will not fail due to lack of memory once that memory has been successfully allocated. VmallocTotal: total size of vmalloc memory area VmallocUsed: amount of vmalloc area which is used VmallocChunk: largest contiguous block of vmalloc area which is free .............................................................................. vmallocinfo: Provides information about vmalloced/vmaped areas. One line per area, containing the virtual address range of the area, size in bytes, caller information of the creator, and optional information depending on the kind of area : pages=nr number of pages phys=addr if a physical address was specified ioremap I/O mapping (ioremap() and friends) vmalloc vmalloc() area vmap vmap()ed pages user VM_USERMAP area vpages buffer for pages pointers was vmalloced (huge area) N=nr (Only on NUMA kernels) Number of pages allocated on memory node > cat /proc/vmallocinfo 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ... /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ... /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f... phys=7fee8000 ioremap 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f... phys=7fee7000 ioremap 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ... /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ... pages=2 vmalloc N1=2 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ... /0x130 [x_tables] pages=4 vmalloc N0=4 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ... pages=14 vmalloc N2=14 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ... pages=4 vmalloc N1=4 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ... pages=2 vmalloc N1=2 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ... pages=10 vmalloc N0=10 .............................................................................. softirqs: Provides counts of softirq handlers serviced since boot time, for each cpu. > cat /proc/softirqs CPU0 CPU1 CPU2 CPU3 HI: 0 0 0 0 TIMER: 27166 27120 27097 27034 NET_TX: 0 0 0 17 NET_RX: 42 0 0 39 BLOCK: 0 0 107 1121 TASKLET: 0 0 0 290 SCHED: 27035 26983 26971 26746 HRTIMER: 0 0 0 0 RCU: 1678 1769 2178 2250 1.3 IDE devices in /proc/ide ---------------------------- The subdirectory /proc/ide contains information about all IDE devices of which the kernel is aware. There is one subdirectory for each IDE controller, the file drivers and a link for each IDE device, pointing to the device directory in the controller specific subtree. The file drivers contains general information about the drivers used for the IDE devices: > cat /proc/ide/drivers ide-cdrom version 4.53 ide-disk version 1.08 More detailed information can be found in the controller specific subdirectories. These are named ide0, ide1 and so on. Each of these directories contains the files shown in table 1-6. Table 1-6: IDE controller info in /proc/ide/ide? .............................................................................. File Content channel IDE channel (0 or 1) config Configuration (only for PCI/IDE bridge) mate Mate name model Type/Chipset of IDE controller .............................................................................. Each device connected to a controller has a separate subdirectory in the controllers directory. The files listed in table 1-7 are contained in these directories. Table 1-7: IDE device information .............................................................................. File Content cache The cache capacity Capacity of the medium (in 512Byte blocks) driver driver and version geometry physical and logical geometry identify device identify block media media type model device identifier settings device setup smart_thresholds IDE disk management thresholds smart_values IDE disk management values .............................................................................. The most interesting file is settings. This file contains a nice overview of the drive parameters: # cat /proc/ide/ide0/hda/settings name value min max mode ---- ----- --- --- ---- bios_cyl 526 0 65535 rw bios_head 255 0 255 rw bios_sect 63 0 63 rw breada_readahead 4 0 127 rw bswap 0 0 1 r file_readahead 72 0 2097151 rw io_32bit 0 0 3 rw keepsettings 0 0 1 rw max_kb_per_request 122 1 127 rw multcount 0 0 8 rw nice1 1 0 1 rw nowerr 0 0 1 rw pio_mode write-only 0 255 w slow 0 0 1 rw unmaskirq 0 0 1 rw using_dma 0 0 1 rw 1.4 Networking info in /proc/net -------------------------------- The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the additional values you get for IP version 6 if you configure the kernel to support this. Table 1-9 lists the files and their meaning. Table 1-8: IPv6 info in /proc/net .............................................................................. File Content udp6 UDP sockets (IPv6) tcp6 TCP sockets (IPv6) raw6 Raw device statistics (IPv6) igmp6 IP multicast addresses, which this host joined (IPv6) if_inet6 List of IPv6 interface addresses ipv6_route Kernel routing table for IPv6 rt6_stats Global IPv6 routing tables statistics sockstat6 Socket statistics (IPv6) snmp6 Snmp data (IPv6) .............................................................................. Table 1-9: Network info in /proc/net .............................................................................. File Content arp Kernel ARP table dev network devices with statistics dev_mcast the Layer2 multicast groups a device is listening too (interface index, label, number of references, number of bound addresses). dev_stat network device status ip_fwchains Firewall chain linkage ip_fwnames Firewall chain names ip_masq Directory containing the masquerading tables ip_masquerade Major masquerading table netstat Network statistics raw raw device statistics route Kernel routing table rpc Directory containing rpc info rt_cache Routing cache snmp SNMP data sockstat Socket statistics tcp TCP sockets udp UDP sockets unix UNIX domain sockets wireless Wireless interface data (Wavelan etc) igmp IP multicast addresses, which this host joined psched Global packet scheduler parameters. netlink List of PF_NETLINK sockets ip_mr_vifs List of multicast virtual interfaces ip_mr_cache List of multicast routing cache .............................................................................. You can use this information to see which network devices are available in your system and how much traffic was routed over those devices: > cat /proc/net/dev Inter-|Receive |[... face |bytes packets errs drop fifo frame compressed multicast|[... lo: 908188 5596 0 0 0 0 0 0 [... ppp0:15475140 20721 410 0 0 410 0 0 [... eth0: 614530 7085 0 0 0 0 0 1 [... ...] Transmit ...] bytes packets errs drop fifo colls carrier compressed ...] 908188 5596 0 0 0 0 0 0 ...] 1375103 17405 0 0 0 0 0 0 ...] 1703981 5535 0 0 0 3 0 0 In addition, each Channel Bond interface has its own directory. For example, the bond0 device will have a directory called /proc/net/bond0/. It will contain information that is specific to that bond, such as the current slaves of the bond, the link status of the slaves, and how many times the slaves link has failed. 1.5 SCSI info ------------- If you have a SCSI host adapter in your system, you'll find a subdirectory named after the driver for this adapter in /proc/scsi. You'll also see a list of all recognized SCSI devices in /proc/scsi: >cat /proc/scsi/scsi Attached devices: Host: scsi0 Channel: 00 Id: 00 Lun: 00 Vendor: IBM Model: DGHS09U Rev: 03E0 Type: Direct-Access ANSI SCSI revision: 03 Host: scsi0 Channel: 00 Id: 06 Lun: 00 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04 Type: CD-ROM ANSI SCSI revision: 02 The directory named after the driver has one file for each adapter found in the system. These files contain information about the controller, including the used IRQ and the IO address range. The amount of information shown is dependent on the adapter you use. The example shows the output for an Adaptec AHA-2940 SCSI adapter: > cat /proc/scsi/aic7xxx/0 Adaptec AIC7xxx driver version: 5.1.19/3.2.4 Compile Options: TCQ Enabled By Default : Disabled AIC7XXX_PROC_STATS : Disabled AIC7XXX_RESET_DELAY : 5 Adapter Configuration: SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter Ultra Wide Controller PCI MMAPed I/O Base: 0xeb001000 Adapter SEEPROM Config: SEEPROM found and used. Adaptec SCSI BIOS: Enabled IRQ: 10 SCBs: Active 0, Max Active 2, Allocated 15, HW 16, Page 255 Interrupts: 160328 BIOS Control Word: 0x18b6 Adapter Control Word: 0x005b Extended Translation: Enabled Disconnect Enable Flags: 0xffff Ultra Enable Flags: 0x0001 Tag Queue Enable Flags: 0x0000 Ordered Queue Tag Flags: 0x0000 Default Tag Queue Depth: 8 Tagged Queue By Device array for aic7xxx host instance 0: {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} Actual queue depth per device for aic7xxx host instance 0: {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} Statistics: (scsi0:0:0:0) Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) Total transfers 160151 (74577 reads and 85574 writes) (scsi0:0:6:0) Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) Total transfers 0 (0 reads and 0 writes) 1.6 Parallel port info in /proc/parport --------------------------------------- The directory /proc/parport contains information about the parallel ports of your system. It has one subdirectory for each port, named after the port number (0,1,2,...). These directories contain the four files shown in Table 1-10. Table 1-10: Files in /proc/parport .............................................................................. File Content autoprobe Any IEEE-1284 device ID information that has been acquired. devices list of the device drivers using that port. A + will appear by the name of the device currently using the port (it might not appear against any). hardware Parallel port's base address, IRQ line and DMA channel. irq IRQ that parport is using for that port. This is in a separate file to allow you to alter it by writing a new value in (IRQ number or none). .............................................................................. 1.7 TTY info in /proc/tty ------------------------- Information about the available and actually used tty's can be found in the directory /proc/tty.You'll find entries for drivers and line disciplines in this directory, as shown in Table 1-11. Table 1-11: Files in /proc/tty .............................................................................. File Content drivers list of drivers and their usage ldiscs registered line disciplines driver/serial usage statistic and status of single tty lines .............................................................................. To see which tty's are currently in use, you can simply look into the file /proc/tty/drivers: > cat /proc/tty/drivers pty_slave /dev/pts 136 0-255 pty:slave pty_master /dev/ptm 128 0-255 pty:master pty_slave /dev/ttyp 3 0-255 pty:slave pty_master /dev/pty 2 0-255 pty:master serial /dev/cua 5 64-67 serial:callout serial /dev/ttyS 4 64-67 serial /dev/tty0 /dev/tty0 4 0 system:vtmaster /dev/ptmx /dev/ptmx 5 2 system /dev/console /dev/console 5 1 system:console /dev/tty /dev/tty 5 0 system:/dev/tty unknown /dev/tty 4 1-63 console 1.8 Miscellaneous kernel statistics in /proc/stat ------------------------------------------------- Various pieces of information about kernel activity are available in the /proc/stat file. All of the numbers reported in this file are aggregates since the system first booted. For a quick look, simply cat the file: > cat /proc/stat cpu 2255 34 2290 22625563 6290 127 456 0 0 cpu0 1132 34 1441 11311718 3675 127 438 0 0 cpu1 1123 0 849 11313845 2614 0 18 0 0 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...] ctxt 1990473 btime 1062191376 processes 2915 procs_running 1 procs_blocked 0 softirq 183433 0 21755 12 39 1137 231 21459 2263 The very first "cpu" line aggregates the numbers in all of the other "cpuN" lines. These numbers identify the amount of time the CPU has spent performing different kinds of work. Time units are in USER_HZ (typically hundredths of a second). The meanings of the columns are as follows, from left to right: - user: normal processes executing in user mode - nice: niced processes executing in user mode - system: processes executing in kernel mode - idle: twiddling thumbs - iowait: waiting for I/O to complete - irq: servicing interrupts - softirq: servicing softirqs - steal: involuntary wait - guest: running a normal guest - guest_nice: running a niced guest The "intr" line gives counts of interrupts serviced since boot time, for each of the possible system interrupts. The first column is the total of all interrupts serviced; each subsequent column is the total for that particular interrupt. The "ctxt" line gives the total number of context switches across all CPUs. The "btime" line gives the time at which the system booted, in seconds since the Unix epoch. The "processes" line gives the number of processes and threads created, which includes (but is not limited to) those created by calls to the fork() and clone() system calls. The "procs_running" line gives the total number of threads that are running or ready to run (i.e., the total number of runnable threads). The "procs_blocked" line gives the number of processes currently blocked, waiting for I/O to complete. The "softirq" line gives counts of softirqs serviced since boot time, for each of the possible system softirqs. The first column is the total of all softirqs serviced; each subsequent column is the total for that particular softirq. 1.9 Ext4 file system parameters ------------------------------ Information about mounted ext4 file systems can be found in /proc/fs/ext4. Each mounted filesystem will have a directory in /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or /proc/fs/ext4/dm-0). The files in each per-device directory are shown in Table 1-12, below. Table 1-12: Files in /proc/fs/ext4/ .............................................................................. File Content mb_groups details of multiblock allocator buddy cache of free blocks .............................................................................. 2.0 /proc/consoles ------------------ Shows registered system console lines. To see which character device lines are currently used for the system console /dev/console, you may simply look into the file /proc/consoles: > cat /proc/consoles tty0 -WU (ECp) 4:7 ttyS0 -W- (Ep) 4:64 The columns are: device name of the device operations R = can do read operations W = can do write operations U = can do unblank flags E = it is enabled C = it is preferred console B = it is primary boot console p = it is used for printk buffer b = it is not a TTY but a Braille device a = it is safe to use when cpu is offline major:minor major and minor number of the device separated by a colon ------------------------------------------------------------------------------ Summary ------------------------------------------------------------------------------ The /proc file system serves information about the running system. It not only allows access to process data but also allows you to request the kernel status by reading files in the hierarchy. The directory structure of /proc reflects the types of information and makes it easy, if not obvious, where to look for specific data. ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ CHAPTER 2: MODIFYING SYSTEM PARAMETERS ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ In This Chapter ------------------------------------------------------------------------------ * Modifying kernel parameters by writing into files found in /proc/sys * Exploring the files which modify certain parameters * Review of the /proc/sys file tree ------------------------------------------------------------------------------ A very interesting part of /proc is the directory /proc/sys. This is not only a source of information, it also allows you to change parameters within the kernel. Be very careful when attempting this. You can optimize your system, but you can also cause it to crash. Never alter kernel parameters on a production system. Set up a development machine and test to make sure that everything works the way you want it to. You may have no alternative but to reboot the machine once an error has been made. To change a value, simply echo the new value into the file. An example is given below in the section on the file system data. You need to be root to do this. You can create your own boot script to perform this every time your system boots. The files in /proc/sys can be used to fine tune and monitor miscellaneous and general things in the operation of the Linux kernel. Since some of the files can inadvertently disrupt your system, it is advisable to read both documentation and source before actually making adjustments. In any case, be very careful when writing to any of these files. The entries in /proc may change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt review the kernel documentation in the directory /usr/src/linux/Documentation. This chapter is heavily based on the documentation included in the pre 2.2 kernels, and became part of it in version 2.2.1 of the Linux kernel. Please see: Documentation/sysctl/ directory for descriptions of these entries. ------------------------------------------------------------------------------ Summary ------------------------------------------------------------------------------ Certain aspects of kernel behavior can be modified at runtime, without the need to recompile the kernel, or even to reboot the system. The files in the /proc/sys tree can not only be read, but also modified. You can use the echo command to write value into these files, thereby changing the default settings of the kernel. ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ CHAPTER 3: PER-PROCESS PARAMETERS ------------------------------------------------------------------------------ 3.1 /proc//oom_score_adj- Adjust the oom-killer score -------------------------------------------------------------------------------- This file can be used to adjust the badness heuristic used to select which process gets killed in out of memory conditions. The badness heuristic assigns a value to each candidate task ranging from 0 (never kill) to 1000 (always kill) to determine which process is targeted. The units are roughly a proportion along that range of allowed memory the process may allocate from based on an estimation of its current memory and swap use. For example, if a task is using all allowed memory, its badness score will be 1000. If it is using half of its allowed memory, its score will be 500. There is an additional factor included in the badness score: root processes are given 3% extra memory over other tasks. The amount of "allowed" memory depends on the context in which the oom killer was called. If it is due to the memory assigned to the allocating task's cpuset being exhausted, the allowed memory represents the set of mems assigned to that cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed memory represents the set of mempolicy nodes. If it is due to a memory limit (or swap limit) being reached, the allowed memory is that configured limit. Finally, if it is due to the entire system being out of memory, the allowed memory represents all allocatable resources. The value of /proc//oom_score_adj is added to the badness score before it is used to determine which task to kill. Acceptable values range from -1000 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This allows userspace to polarize the preference for oom killing either by always preferring a certain task or completely disabling it. The lowest possible value, -1000, is equivalent to disabling oom killing entirely for that task since it will always report a badness score of 0. Consequently, it is very simple for userspace to define the amount of memory to consider for each task. Setting a /proc//oom_score_adj value of +500, for example, is roughly equivalent to allowing the remainder of tasks sharing the same system, cpuset, mempolicy, or memory controller resources to use at least 50% more memory. A value of -500, on the other hand, would be roughly equivalent to discounting 50% of the task's allowed memory from being considered as scoring against the task. The value of /proc//oom_score_adj may be reduced no lower than the last value set by a CAP_SYS_RESOURCE process. To reduce the value any lower requires CAP_SYS_RESOURCE. Caveat: when a parent task is selected, the oom killer will sacrifice any first generation children with separate address spaces instead, if possible. This avoids servers and important system daemons from being killed and loses the minimal amount of work. 3.2 /proc//oom_score - Display current oom-killer score ------------------------------------------------------------- This file can be used to check the current score used by the oom-killer is for any given . 3.3 /proc//io - Display the IO accounting fields ------------------------------------------------------- This file contains IO statistics for each running process Example ------- test:/tmp # dd if=/dev/zero of=/tmp/test.dat & [1] 3828 test:/tmp # cat /proc/3828/io rchar: 323934931 wchar: 323929600 syscr: 632687 syscw: 632675 read_bytes: 0 write_bytes: 323932160 cancelled_write_bytes: 0 Description ----------- rchar ----- I/O counter: chars read The number of bytes which this task has caused to be read from storage. This is simply the sum of bytes which this process passed to read() and pread(). It includes things like tty IO and it is unaffected by whether or not actual physical disk IO was required (the read might have been satisfied from pagecache) wchar ----- I/O counter: chars written The number of bytes which this task has caused, or shall cause to be written to disk. Similar caveats apply here as with rchar. syscr ----- I/O counter: read syscalls Attempt to count the number of read I/O operations, i.e. syscalls like read() and pread(). syscw ----- I/O counter: write syscalls Attempt to count the number of write I/O operations, i.e. syscalls like write() and pwrite(). read_bytes ---------- I/O counter: bytes read Attempt to count the number of bytes which this process really did cause to be fetched from the storage layer. Done at the submit_bio() level, so it is accurate for block-backed filesystems. write_bytes ----------- I/O counter: bytes written Attempt to count the number of bytes which this process caused to be sent to the storage layer. This is done at page-dirtying time. cancelled_write_bytes --------------------- The big inaccuracy here is truncate. If a process writes 1MB to a file and then deletes the file, it will in fact perform no writeout. But it will have been accounted as having caused 1MB of write. In other words: The number of bytes which this process caused to not happen, by truncating pagecache. A task can cause "negative" IO too. If this task truncates some dirty pagecache, some IO which another task has been accounted for (in its write_bytes) will not be happening. We _could_ just subtract that from the truncating task's write_bytes, but there is information loss in doing that. Note ---- At its current implementation state, this is a bit racy on 32-bit machines: if process A reads process B's /proc/pid/io while process B is updating one of those 64-bit counters, process A could see an intermediate result. More information about this can be found within the taskstats documentation in Documentation/accounting. 3.4 /proc//coredump_filter - Core dump filtering settings --------------------------------------------------------------- When a process is dumped, all anonymous memory is written to a core file as long as the size of the core file isn't limited. But sometimes we don't want to dump some memory segments, for example, huge shared memory. Conversely, sometimes we want to save file-backed memory segments into a core file, not only the individual files. /proc//coredump_filter allows you to customize which memory segments will be dumped when the process is dumped. coredump_filter is a bitmask of memory types. If a bit of the bitmask is set, memory segments of the corresponding memory type are dumped, otherwise they are not dumped. The following 7 memory types are supported: - (bit 0) anonymous private memory - (bit 1) anonymous shared memory - (bit 2) file-backed private memory - (bit 3) file-backed shared memory - (bit 4) ELF header pages in file-backed private memory areas (it is effective only if the bit 2 is cleared) - (bit 5) hugetlb private memory - (bit 6) hugetlb shared memory Note that MMIO pages such as frame buffer are never dumped and vDSO pages are always dumped regardless of the bitmask status. Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only effected by bit 5-6. Default value of coredump_filter is 0x23; this means all anonymous memory segments and hugetlb private memory are dumped. If you don't want to dump all shared memory segments attached to pid 1234, write 0x21 to the process's proc file. $ echo 0x21 > /proc/1234/coredump_filter When a new process is created, the process inherits the bitmask status from its parent. It is useful to set up coredump_filter before the program runs. For example: $ echo 0x7 > /proc/self/coredump_filter $ ./some_program 3.5 /proc//mountinfo - Information about mounts -------------------------------------------------------- This file contains lines of the form: 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue (1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11) (1) mount ID: unique identifier of the mount (may be reused after umount) (2) parent ID: ID of parent (or of self for the top of the mount tree) (3) major:minor: value of st_dev for files on filesystem (4) root: root of the mount within the filesystem (5) mount point: mount point relative to the process's root (6) mount options: per mount options (7) optional fields: zero or more fields of the form "tag[:value]" (8) separator: marks the end of the optional fields (9) filesystem type: name of filesystem of the form "type[.subtype]" (10) mount source: filesystem specific information or "none" (11) super options: per super block options Parsers should ignore all unrecognised optional fields. Currently the possible optional fields are: shared:X mount is shared in peer group X master:X mount is slave to peer group X propagate_from:X mount is slave and receives propagation from peer group X (*) unbindable mount is unbindable (*) X is the closest dominant peer group under the process's root. If X is the immediate master of the mount, or if there's no dominant peer group under the same root, then only the "master:X" field is present and not the "propagate_from:X" field. For more information on mount propagation see: Documentation/filesystems/sharedsubtree.txt 3.6 /proc//comm & /proc//task//comm -------------------------------------------------------- These files provide a method to access a tasks comm value. It also allows for a task to set its own or one of its thread siblings comm value. The comm value is limited in size compared to the cmdline value, so writing anything longer then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated comm value. 3.7 /proc//task//children - Information about task children ------------------------------------------------------------------------- This file provides a fast way to retrieve first level children pids of a task pointed by / pair. The format is a space separated stream of pids. Note the "first level" here -- if a child has own children they will not be listed here, one needs to read /proc//task//children to obtain the descendants. Since this interface is intended to be fast and cheap it doesn't guarantee to provide precise results and some children might be skipped, especially if they've exited right after we printed their pids, so one need to either stop or freeze processes being inspected if precise results are needed. ------------------------------------------------------------------------------ Configuring procfs ------------------------------------------------------------------------------ 4.1 Mount options --------------------- The following mount options are supported: hidepid= Set /proc// access mode. gid= Set the group authorized to learn processes information. hidepid=0 means classic mode - everybody may access all /proc// directories (default). hidepid=1 means users may not access any /proc// directories but their own. Sensitive files like cmdline, sched*, status are now protected against other users. This makes it impossible to learn whether any user runs specific program (given the program doesn't reveal itself by its behaviour). As an additional bonus, as /proc//cmdline is unaccessible for other users, poorly written programs passing sensitive information via program arguments are now protected against local eavesdroppers. hidepid=2 means hidepid=1 plus all /proc// will be fully invisible to other users. It doesn't mean that it hides a fact whether a process with a specific pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by stat()'ing /proc// otherwise. It greatly complicates an intruder's task of gathering information about running processes, whether some daemon runs with elevated privileges, whether other user runs some sensitive program, whether other users run any program at all, etc. gid= defines a group authorized to learn processes information otherwise prohibited by hidepid=. If you use some daemon like identd which needs to learn information about processes information, just add identd to this group.