p-commands

p-Commands

In Unix, every object is either a file or a process. With the /proc virtual file system, even processes may be treated like files.

/proc (or procfs) is a virtual file system that allows us to examine processes like files. This means that /proc allows us to use file-like operations and intuitions when looking at processes. /proc does not occupy disk space; it is located in working memory. This structure was originally designed as a programming interface for writing debuggers, but it has grown considerably since then.

To avoid confusion, we will refer to the virtual file system as /proc or procfs. The man page for procfs is proc(4). proc, on the other hand, will be used to refer to the process data structure discussed in the Process Structure page.

Under /proc is a list of numbers, each of which is a Process ID (PID) for a process on our system. Under these directories are subdirectories referring to the different components of interest of each process. This directory structure can be examined directly, but we usually prefer to use commands written to extract information from this structure. These are known as the p-commands.

• pcred: Display process credentials (eg EUID/EGID, RUID/RGID, saved UIDs/GIDs)
• pfiles: Reports fstat() and fcntl() information for all open files. This includes information on the inode number, file system, ownership and size.
• pflags: Prints the tracing flags, pending and held signals and other /proc status information for each LWP.
• pgrep: Finds processes matching certain criteria.
• pkill: Kills specified processes.
• pldd: Lists dynamic libraries linked to the process.
• pmap: Prints process address space map.
• prun: Starts stopped processes.
• prstat: Display process performance-related statistics.
• ps: List process information.
• psig: Lists signal actions.
• pstack: Prints a stack trace for each LWP in the process.
• pstop: Stops the process.
• ptime: Times the command; does not time children.
• ptree: Prints process genealogy.
• pwait: Wait for specified processes to complete.
• pwdx: Prints process working directory.

prstat Example 1

CPU Saturation is can be directly measured via prstat. (Saturation refers to a situation where there is not enough CPU capacity to adequately handle requests for processing resources.) Saturation can be measured directly by looking at the CPU latency time for each thread reported by prstat -mL. (LAT is reported as a percentage of the time that a thread is waiting to use a processor.)

This example shows the prstat -mL output from a single-CPU system that has been overloaded. Notice the load average and LAT numbers.

PID USERNAME USR SYS TRP TFL DFL LCK SLP LAT VCX ICX SCL SIG PROCESS/LWPID
2724 root 24 0.2 0.0 0.0 0.0 0.0 2.2 74 284 423 361 0 gzip/1
2729 root 21 0.3 0.0 0.0 0.0 0.0 3.3 75 396 564 518 0 gzip/1
2733 root 20 0.3 0.0 0.0 0.0 0.0 5.3 75 391 514 484 0 gzip/1
2737 root 14 0.2 0.0 0.0 0.0 0.0 4.1 81 176 415 383 0 gzip/1
2730 root 3.3 0.3 0.0 0.0 0.0 0.0 96 0.7 602 258 505 0 gunzip/1
2734 root 2.9 0.3 0.0 0.0 0.0 0.0 92 4.5 522 280 457 0 gunzip/1
2738 root 2.7 0.2 0.0 0.0 0.0 0.0 93 3.9 377 147 370 0 gunzip/1
2725 root 2.4 0.2 0.0 0.0 0.0 0.0 95 2.4 495 179 355 0 gunzip/1
2728 root 0.1 1.4 0.0 0.0 0.0 0.0 97 1.7 769 11 2K 0 tar/1
2732 root 0.1 1.3 0.0 0.0 0.0 0.0 99 0.2 762 14 2K 0 tar/1
2723 root 0.0 1.1 0.0 0.0 0.0 0.0 99 0.1 564 7 1K 0 tar/1
2731 root 0.3 0.4 0.0 0.0 0.0 0.0 98 1.2 754 3 1K 0 tar/1
2735 root 0.3 0.4 0.0 0.0 0.0 0.0 98 0.9 722 0 1K 0 tar/1
2736 root 0.0 0.6 0.0 0.0 0.0 0.0 99 0.0 341 2 1K 0 tar/1
2726 root 0.3 0.3 0.0 0.0 0.0 0.0 98 1.0 473 145 1K 0 tar/1
2739 root 0.2 0.2 0.0 0.0 0.0 0.0 99 0.3 335 1 664 0 tar/1
2749 scromar 0.0 0.1 0.0 0.0 0.0 0.0 100 0.0 23 0 194 0 prstat/1
337 root 0.0 0.0 0.0 0.0 0.0 0.0 100 0.0 6 0 36 6 xntpd/1
2716 scromar 0.0 0.0 0.0 0.0 0.0 0.0 100 0.0 3 1 21 0 sshd/1
124 root 0.0 0.0 0.0 0.0 0.0 0.0 100 0.0 3 0 17 0 picld/4
119 root 0.0 0.0 0.0 0.0 0.0 0.0 100 0.0 21 0 63 0 nscd/26
Total: 51 processes, 164 lwps, load averages: 4.12, 2.13, 0.88


prstat Example 2

In this case, we sort prstat output to look for the processes with heavy memory utilization:

# prstat -s rss
PID USERNAME SIZE RSS STATE PRI NICE TIME CPU PROCESS/NLWP
471 juser 125M 58M sleep 59 0 4:26:46 0.6% java/17
200 daemon 62M 55M sleep 59 0 0:01:21 0.0% nfsmapid/4
18296 juser 116M 39M sleep 26 11 0:05:36 0.1% java/23
...
254 root 3968K 1016K sleep 59 0 0:00:03 0.0% sshd/1
Total: 47 processes, 221 lwps, load averages: 0.20, 0.21, 0.20


Other Usage Examples

# ps -ef | grep more | grep -v grep
root 18494 8025 0 08:53:09 pts/3 0:00 more
# pgrep more
18494
# pmap -x 18494
18494: more
Address Kbytes RSS Anon Locked Mode Mapped File
00010000 32 32 - - r-x-- more
00028000 8 8 8 - rwx-- more
0002A000 16 16 16 - rwx-- [ heap ]
FF200000 864 824 - - r-x-- libc.so.1
FF2E8000 32 32 32 - rwx-- libc.so.1
FF2F0000 8 8 8 - rwx-- libc.so.1
FF300000 16 16 - - r-x-- en_US.ISO8859-1.so.3
FF312000 16 16 16 - rwx-- en_US.ISO8859-1.so.3
FF330000 8 8 - - r-x-- libc_psr.so.1
FF340000 8 8 8 - rwx-- [ anon ]
FF350000 168 104 - - r-x-- libcurses.so.1
FF38A000 32 32 24 - rwx-- libcurses.so.1
FF392000 8 8 8 - rwx-- libcurses.so.1
FF3A0000 24 16 16 - rwx-- [ anon ]
FF3B0000 184 184 - - r-x-- ld.so.1
FF3EE000 8 8 8 - rwx-- ld.so.1
FF3F0000 8 8 8 - rwx-- ld.so.1
FFBFC000 16 16 16 - rw--- [ stack ]
-------- ------- ------- ------- -------
total Kb 1456 1344 168 -
# pstack 18494
18494: more
ff2c0c7c read (2, ffbff697, 1)
00015684 ???????? (0, 1, 43858, ff369ad4, 0, 28b20)
000149a4 ???????? (ffbff82f, 28400, 15000000, 28af6, 0, 28498)
00013ad8 ???????? (0, 28b10, 28c00, 400b0, ff2a4a74, 0)
00012780 ???????? (2a078, ff393050, 0, 28b00, 2a077, 6b)
00011c68 main (28b10, ffffffff, 28c00, 0, 0, 1) + 684
000115cc _start (0, 0, 0, 0, 0, 0) + 108
# pfiles 18494
18494: more
Current rlimit: 256 file descriptors
0: S_IFIFO mode:0000 dev:292,0 ino:2083873 uid:0 gid:0 size:0
O_RDWR
1: S_IFCHR mode:0620 dev:284,0 ino:12582922 uid:1000 gid:7 rdev:24,3
O_RDWR|O_NOCTTY|O_LARGEFILE
/devices/pseudo/pts@0:3
2: S_IFCHR mode:0620 dev:284,0 ino:12582922 uid:1000 gid:7 rdev:24,3
O_RDWR|O_NOCTTY|O_LARGEFILE
/devices/pseudo/pts@0:3
# pcred 18494
18494: e/r/suid=0 e/r/sgid=0
groups: 0 1 2 3 4 5 6 7 8 9 12