proc file system in Linux
Proc file system (procfs) is virtual file system created on fly when system boots and is dissolved at time of system shut down.
It contains useful information about the processes that are currently running, it is regarded as control and information center for kernel.
The proc file system also provides communication medium between kernel space and user space.
Below is snapshot of /proc from my PC.
ls -l /proc total 0 dr-xr-xr-x 9 root root 0 Mar 31 21:34 1 dr-xr-xr-x 9 root root 0 Mar 31 21:34 10 dr-xr-xr-x 9 avahi avahi 0 Mar 31 21:34 1034 dr-xr-xr-x 9 root root 0 Mar 31 21:34 1036 dr-xr-xr-x 9 root root 0 Mar 31 21:34 1039 dr-xr-xr-x 9 root root 0 Mar 31 21:34 1041 dr-xr-xr-x 9 root root 0 Mar 31 21:34 1043 dr-xr-xr-x 9 root root 0 Mar 31 21:34 1044 dr-xr-xr-x 9 root root 0 Mar 31 21:34 1048 dr-xr-xr-x 9 root root 0 Mar 31 21:34 105 dr-xr-xr-x 9 root root 0 Mar 31 21:34 1078 dr-xr-xr-x 9 root root 0 Mar 31 21:34 11 dr-xr-xr-x 9 root root 0 Mar 31 21:34 1121 dr-xr-xr-x 9 lp lp 0 Mar 31 21:34 1146 dr-xr-xr-x 9 postgres postgres 0 Mar 31 21:34 1149 dr-xr-xr-x 9 mysql mysql 0 Mar 31 21:34 1169 dr-xr-xr-x 9 postgres postgres 0 Mar 31 21:34 1180 dr-xr-xr-x 9 postgres postgres 0 Mar 31 21:34 1181 dr-xr-xr-x 9 postgres postgres 0 Mar 31 21:34 1182 dr-xr-xr-x 9 postgres postgres 0 Mar 31 21:34 1183 dr-xr-xr-x 9 postgres postgres 0 Mar 31 21:34 1184 dr-xr-xr-x 9 root root 0 Mar 31 21:34 1186 dr-xr-xr-x 9 root root 0 Mar 31 21:34 12 ...
If you list the directories, you will find that for each PID of a process there is dedicated directory.
You can check directories only on terminal using
ls -l /proc | grep '^d'
Now let’s check for particular process of assigned PID, you can get the PID of any running process from ps command
ps -aux
Output:
ps -aux command output
Now check the highlighted process with PID=7494, you can check that there is entry for this process in /proc file system.
ls -ltr /proc/7494
Output:
total 0 -rw-r--r-- 1 mandeep mandeep 0 Apr 1 01:14 oom_score_adj dr-xr-xr-x 13 mandeep mandeep 0 Apr 1 01:14 task -r--r--r-- 1 mandeep mandeep 0 Apr 1 01:16 status -r--r--r-- 1 mandeep mandeep 0 Apr 1 01:16 stat -r--r--r-- 1 mandeep mandeep 0 Apr 1 01:16 cmdline -r--r--r-- 1 mandeep mandeep 0 Apr 1 01:17 wchan -rw-r--r-- 1 mandeep mandeep 0 Apr 1 01:17 uid_map -rw-rw-rw- 1 mandeep mandeep 0 Apr 1 01:17 timerslack_ns -r--r--r-- 1 mandeep mandeep 0 Apr 1 01:17 timers -r-------- 1 mandeep mandeep 0 Apr 1 01:17 syscall -r--r--r-- 1 mandeep mandeep 0 Apr 1 01:17 statm -r-------- 1 mandeep mandeep 0 Apr 1 01:17 stack -r--r--r-- 1 mandeep mandeep 0 Apr 1 01:17 smaps -rw-r--r-- 1 mandeep mandeep 0 Apr 1 01:17 setgroups -r--r--r-- 1 mandeep mandeep 0 Apr 1 01:17 sessionid -r--r--r-- 1 mandeep mandeep 0 Apr 1 01:17 schedstat -rw-r--r-- 1 mandeep mandeep 0 Apr 1 01:17 sched lrwxrwxrwx 1 mandeep mandeep 0 Apr 1 01:17 root -> /proc/2341/fdinfo -rw-r--r-- 1 mandeep mandeep 0 Apr 1 01:17 projid_map -r-------- 1 mandeep mandeep 0 Apr 1 01:17 personality ...
In linux, /proc includes a directory for each running process, including kernel processes, in directories named /proc/PID, these are the directories present:
| directory | description |
|---|---|
| /proc/PID/cmdline | Command line arguments. |
| /proc/PID/cpu | Current and last cpu in which it was executed. |
| /proc/PID/cwd | Link to the current working directory. |
| /proc/PID/environ | Values of environment variables. |
| /proc/PID/exe | Link to the executable of this process. |
| /proc/PID/fd | Directory, which contains all file descriptors. |
| /proc/PID/maps | Memory maps to executables and library files. |
| /proc/PID/mem | Memory held by this process. |
| /proc/PID/root | Link to the root directory of this process. |
| /proc/PID/stat | Process status. |
| /proc/PID/statm | Process memory status information. |
| /proc/PID/status | Process status in human readable form. |
Some other files in /proc file system are:
| file | description |
|---|---|
| /proc/crypto | list of available cryptographic modules |
| /proc/diskstats | information (including device numbers) for each of the logical disk devices |
| /proc/filesystems | list of the file systems supported by the kernel at the time of listing |
| /proc/kmsg | holding messages output by the kernel |
| /proc/meminfo | summary of how the kernel is managing its memory. |
| /proc/scsi | information about any devices connected via a SCSI or RAID controller |
| /proc/tty | information about the current terminals |
| /proc/version | containing the Linux kernel version, distribution number, gcc version number (used to build the kernel) and any other pertinent information relating to the version of the kernel currently running |
For example, the contents of /proc/crypto are
less /proc/crypto name : ccm(aes) driver : ccm_base(ctr(aes-aesni), cbcmac(aes-aesni)) module : ccm priority : 300 refcnt : 2 selftest : passed internal : no type : aead async : no blocksize : 1 ivsize : 16 maxauthsize : 16 geniv : name : ctr(aes) driver : ctr(aes-aesni) module : kernel priority : 300 refcnt : 3 selftest : passed internal : no type : blkcipher blocksize : 1 min keysize : 16 max keysize : 32 ivsize : 16 geniv : chainiv ...
References :
1) /wiki/Procfs
2) /proc
Please Login to comment...