Date : 11-10-15 00:00
System Monitoring Commands for Linux
 Author : 07 (141.♡.210.218)
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   http://unixgeeks.org/security/newbie/unix/man9/misc3.html [2148]
newbie: System Monitoring commands - du, df, ps, top, who, w, free.
Date: 24-Dec-99
Author: cogNiTioN <cognition@bigfoot.com>

System Monitoring Commands

This file goes through some commands that can let you know what your system
is doing. Using these commands you can tell what programs are running, how
much memory or how many cpu cycles those programs are using, who's logged
in, where from, how long they've been logged in for and more. These
commands also deal with how much disk space or memory is being used.

Bear in mind that this is not a detailed look at each command, it is an
overview only.

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Command: du

This command prints the disk usage (in Kb) of each directory and it's sub
directories. By default it starts from the current directory, but supplying
the name of a directory after the command will make it start from that
directory.

cognition@pingu:/usr/cog $ du

126 ./Mail/.archived/.pgp
18851 ./Mail/.archived
21016 ./Mail
2247 ./zip
80 ./.pgp
15 ./develop/getmail/bup
35 ./develop/getmail
36 ./develop
2300 ./.procmail
~~
<SNIPPED FULL OUTPUT OF COMMAND, FOR BREVITY>
~~
31678 .

cognition@pingu:/usr/cog $ du Mail

126 Mail/.archived/.pgp
18851 Mail/.archived
21016 Mail

cognition@pingu:/usr/cog $ du /root

du: /root: Permission denied


As the last example shows, you can only show the disk usage for
directories (or subdirectories) that you have execute permissions on.

Options: (these may vary depending on version run, and there are more ;)
-a (--all) Prints usage for ALL files, not just the subdirectories
-b (--bytes) Prints usage in bytes rather than Kb.
-s (--summarize) Prints ONLY the total usage of the directory

Consult 'man du' for more details on usage

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Command: df

This command tells you the amount of free space on all mounted file systems,
or you can specify the name of a device you want to check, (the device has
to be mounted, though).

cognition@pingu:/usr/cog $ df

Filesystem        1024-blocks  Used Available Capacity Mounted on
/dev/hdb1            483038  358274    99816    78%  /
/dev/hda1            246854  14293  219812      6%  /home
/dev/sda4              98078  96752    1326    99%  /zip

cognition@pingu:/usr/cog $ df /dev/hdb1

Filesystem        1024-blocks  Used Available Capacity Mounted on
/dev/hdb1            483038  358274    99816    78%  /


I currently have 3 file systems mounted (2 internal Hard Discs and a zip
disc). The second column (labeled 1024-blocks) shows the total size (in Kb)
of the corresponding file system, the third column shows how much space has
been used, column four gives the remaining space and column five (Capacity)
shows (as a percentage how much of the space has been used. The last column
simply shows the mount point of that file system.

for more information see 'man df'

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Command: ps

'ps' shows you what processes (programs) you have running (or are running
with your user id).

cognition@pingu:/usr/cog $ ps

  PID TTY STAT TIME COMMAND
32042  1 S    0:04 -bash
32068  2 S    0:04 (bash)
32168  2 S    1:07 vi admin101
32415  2 S    0:00 /bin/bash -c (ps) >/tmp/voa32168 2>&1
32416  2 R    0:00 ps


It's interesting to note the second line up from the bottom; that's what
vi sends out when I get it to execute a command for me.

Note: When using options with ps, you do not need to include a leading
'-' sign, while this is still accepted, it's use is "deprecated".

A good set of options to use is 'aux'. The command 'ps aux' gives you a
surplus of information about all the processes running on your system. Note
you do not need to be 'root' to run 'ps aux', you can do so as a normal user
and still get a full listing of processes. The output from 'ps aux' is
similar to that from the 'top' command, which is covered below, except that
'ps aux' is a snap shot, and is not updated.

See 'man ps' for more information.

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Command: who

As Unix is a multi-user operating system, there can be more than one
person using the machine at any given time. How do you find out how many
users your system currently has? You ask the system, that's how. The 'who'
command shows you who has logged in, where they're logged into and when
they logged in.


cognition@pingu:/usr/cog $ who

cognitio tty1    Sep  6 14:23
cognitio tty2    Sep  6 18:01
root    tty5    Sep  6 18:18


'who' can also tell you who you are, when run as 'who am i', this is the
same as the command 'whoami'.

For more information, including other options, see 'man who'

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Command: w

The 'w' command is really the output of 'uptime', 'who' and 'ps a' combined
to give a comprehensive system usage summary. To give the usage of one
user, just give the user's name after the command.


cognition@pingu:/usr/cog $ w
  9:29pm  up 45 days,  9:59,  4 users,  load average: 1.06, 0.97, 0.92
USER    TTY      FROM              LOGIN@  IDLE  JCPU  PCPU  WHAT
cognitio tty1                      2:23pm  1:54  6.01s  0.70s  -bash
cognitio tty2                      6:01pm  3.00s  1:45  1:39  vi admin101
root    tty5                      6:18pm 36:09  4.35s  4.35s  -bash

cognition@pingu:/usr/cog $ w root
  9:29pm  up 45 days, 10:00,  4 users,  load average: 1.16, 1.01, 0.93
USER    TTY      FROM              LOGIN@  IDLE  JCPU  PCPU  WHAT
root    tty5                      6:18pm 36:56  4.35s  4.35s  -bash



Notice that most entries don't have an entry in the FROM column, this
indicates that they're logged on from the console (i.e. they have physical
access to the machine).

See 'man w' for more details.

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Command: free

'free' shows you information about the machine's memory. This includes
physical memory (RAM), swap as well as the shared memory and buffers
used by the kernal. All measurements are in Kb.


cognition@pingu:/usr/cog $ free
            total      used      free    shared    buffers    cached
Mem:        10672      10168        504      4912        172      3000
-/+ buffers/cache:      6996      3676
Swap:        33228      18068      15160



For more information, and a list of options, see 'man free'

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Command: top

'top' provides lots of information on the processes running, including the
percentage of the cpu and the memory being consumed by that process, who
'owns' the process and it's pid (Process ID), it also shows the output of
'uptime' and a summary of memory usage, similar to 'free'. The output of
'top' is full screen, and refreshes itself frequently (or at user definable
intervals).

Here is a representation of the output from 'top':

cognition@pingu:/usr/cog $ top

11:42pm  up 45 days, 12:13,  9 users,  load average: 1.66, 1.52, 1.20
66 processes: 64 sleeping, 2 running, 0 zombie, 0 stopped
CPU states: 84.5% user, 36.1% system,  0.0% nice,  0.0% idle
Mem:  10672K av,  10276K used,    396K free,  5660K shrd,    212K buff
Swap:  33228K av,  18976K used,  14252K free                  2556K cached

PID USER    PRI  NI  SIZE  RSS SHARE STAT  LIB %CPU %MEM  TIME COMMAND
  216 root      10  0  376  324  192 S      0 32.5  3.0 13267m top
32609 cognitio  9  0  584  584  420 S      0 31.7  5.4  0:29 top
  213 root      20  0  696  596  124 R      0 28.5  5.5 28197m smartbee
32612 cognitio  15  0  580  580  416 R      0 26.6  5.4  0:03 top
32469 root      1  0  208  112    88 S      0  0.7  1.0  0:15 in.telnetd
    3 root    -12 -12    0    0    0 SW<    0  0.1  0.0  3:19 kswapd
  15 root      0  0    84  48    32 S      0  0.1  0.4  18:06 update
32468 cognitio  0  0  204  108    72 S      0  0.1  1.0  0:16 telnet
    1 root      0  0    88  48    24 S      0  0.0  0.4  0:19 init
    2 root      0  0    0    0    0 SW      0  0.0  0.0  1:01 kflushd
    4 root      0  0    0    0    0 SW      0  0.0  0.0  0:00 nfsiod
    5 root      0  0    0    0    0 SW      0  0.0  0.0  0:00 nfsiod
    6 root      0  0    0    0    0 SW      0  0.0  0.0  0:00 nfsiod
    7 root      0  0    0    0    0 SW      0  0.0  0.0  0:00 nfsiod
32042 cognitio  0  0  448  32    32 S      0  0.0  0.2  0:05 bash
32068 cognitio  0  0  408    0    0 SW      0  0.0  0.0  0:04 bash
32071 cognitio  0  0  456  28    28 S      0  0.0  0.2  0:06 bash

For more information, see 'man top'

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See also:
Linux in a Nutshell (O'Reilly)
The Man pages for relevent commands

Please direct any feedback relating to this file to me, via email to: 
<cognition@bigfoot.com>

  -------------------------------------------------------------------------
cogNiTioN <cognition@bigfoot.com>
Copyright 1999 cogNiTioN

 
 

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