List of Linux commands that are used for Server administration

Checking running Process on the server. [ ps, pstree ]

ps

This command is used to check the process running on the server. " ps " command will list all the running process with there respective process ID.

Example:
root@server [~]$ ps
PID TTY TIME CMD
22438 pts/3 00:00:00 su
22439 pts/3 00:00:00 bash
22517 pts/3 00:00:00 psUse the following option to get more process information from the " ps " commands,
root@server [~]$ ps -aux

Also you can grep any particular process on the server.
root@server [~]$ ps -aux | grep exim

pstree

This command is also used the check the process on the server. " pstree " command will list all the running process in the form of a tree structure.

Example:
root@server [~]$ pstree
init─┬─agetty
├─antirelayd
├─bdflush
├─chkservd
├─4*[courierlogger───couriertcpd]
├─courierlogger───authdaemond───5*[authdaemond───authProg]
├─cpanellogd
├─cpdavd
├─cphulkd.pl
├─cpsrvd-ssl───cpsrvd-ssl
├─crond
├─entropychat
├─exim───exim─┬─3*[exim]
│ └─spamc
├─2*[exim]
├─exim───20*[exim]
├─eximstats
├─hpt_wt
├─httpd───56*[httpd]
├─interchange
├─keventd
├─7*[kjournald]
├─klogd
├─ksoftirqd_CPU0
├─ksoftirqd_CPU1
├─ksoftirqd_CPU2
├─ksoftirqd_CPU3
├─kswapd
├─kupdated
├─mailmanctl───8*[python2.4]
├─mdrecoveryd
├─6*[mingetty]
├─mysqld_safe───mysqld───mysqld───26*[mysqld]
├─named───named───6*[named]
├─portsentry
├─pure-authd
├─pure-ftpd
├─10*[python2.4]
├─scsi_eh_0
├─spamd───2*[spamd]
├─ssh
├─sshd─┬─sshd───sshd───bash───su───bash
│ └─sshd───sshd───bash───su───bash───pstree
├─syslogd
└─xinetd

root@server [~]$ pstree -p
init(1)─┬─agetty(7480)
├─antirelayd(8658)
├─bdflush(8)
├─chkservd(6224)
├─courierlogger(6833)───couriertcpd(6834)
├─courierlogger(6840)───couriertcpd(6841)
├─courierlogger(6846)───couriertcpd(6847)
├─courierlogger(6852)───couriertcpd(6853)
├─courierlogger(6858)───authdaemond(6859)─┬─authdaemond(6873)
│ ├─authdaemond(6874)───authProg(26164)
│ ├─authdaemond(6875)───authProg(17488)
│ ├─authdaemond(6876)───authProg(8194)
│ └─authdaemond(6877)───authProg(29956)

Load on a server [ top, w , uptime ]

top

This command is used to find the load on the server. " top " command can also be used to find the process and users that causes load on the server. It gives information about the total process, sleeping process, the zombie process etc.

Example:

root@server [~]$ top -cd3

11:32:03 up 15 days, 23:57, 2 users, load average: 4.95, 5.13, 5.94

root@server [~]$ top -c

top - 07:08:05 up 59 min,  3 users,  load average: 1.07, 1.03, 0.98

Tasks: 126 total,   2 running, 124 sleeping,   0 stopped,   0 zombie

Cpu(s): 35.1%us,  5.4%sy,  0.0%ni, 41.9%id, 16.9%wa,  0.0%hi,  0.7%si,  0.0%st

Mem:    507680k total,   491248k used,    16432k free,     2336k buffers

Swap:  1477940k total,   192688k used,  1285252k free,   136372k cached

 PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                                                            

 3534 root      20   0  386m 121m  13m S 17.6 24.6  10:46.13 /usr/lib/firefox-3.6.10/firefox-bin                                                                                 

 2558 root      20   0  212m  30m 8256 R  9.5  6.2   3:20.31 /usr/X11R6/bin/X :0 -br -audit 0 -auth /var/lib/gdm/:0.Xauth -nolisten tcp vt7                                      

 3399 root      20   0 22332 8672 5612 S  4.1  1.7   0:07.63 /usr/bin/metacity --replace                                                                                         

 6346 root      20   0  103m  22m  16m S  2.0  4.5   0:05.58 /opt/google/chrome/chrome --type=plugin --plugin-path=/opt/google/chrome/libgcflashplayer.so --lang=en-US --plugin-d

 6381 root       20   0  2452 1184  904 R  0.7  0.2   0:00.05 top -c                                                                                                              

    1 root      20   0  3088  396  344 S  0.0  0.1   0:01.28 /sbin/init                                                                                                          

    2 root      15  -5     0    0    0 S  0.0  0.0   0:00.00 [kthreadd]                                                                                                         

    3 root      RT  -5     0    0    0 S  0.0  0.0   0:00.00 [migration/0]                                                                                                       

    4 root      15  -5     0    0    0 S  0.0  0.0   0:00.12 [ksoftirqd/0]                                                                                                      

    5 root      RT  -5     0    0    0 S  0.0  0.0   0:00.00 [watchdog/0]                                                                                                        

FUSER Command :

This command is used to see how many number of  users are using http process  at the same time.

root@server [~]$ fuser -v /hsphere/shared/apache2/bin/httpd.prrefork 

                     USER        PID ACCESS COMMAND

/hsphere/shared/apache2/bin/httpd.prefork

                     root      17392 ...e.  httpd.prefork

                     httpd     23461 ...e.  httpd.prefork

                     httpd     24865 ...e.  httpd.prefork

                     httpd     25090 ...e.  httpd.prefork

                     httpd     25131 ...e.  httpd.prefork

                     httpd     25132 ...e.  httpd.prefork

                     httpd     25329 ...e.  httpd.prefork

                     httpd     25330 ...e.  httpd.prefork

                     httpd     25370 ...e.  httpd.prefork

                     httpd     25372 ...e.  httpd.prefork

                     httpd     25376 ...e.  httpd.prefork

                     httpd     25377 ...e.  httpd.prefork

                     httpd     25378 ...e.  httpd.prefork

w

This command is also find the load and users on the server. " w " command will provide a brief description about the load, time, number of users and the uptime of the server.

Example:

root@server [~]$ w

11:39:18 up 16 days, 4 min, 2 users, load average: 5.33, 5.37, 5.74

USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT

user1 pts/0 user - ip1 8:26am 3:13m 0.09s 0.00s sshd: user1 [priv]

user2 pts/3 user - ip2 11:09am 0.00s 0.13s 0.02s sshd: user2 [priv]

uptime

This command gives the basic information about the uptime and load of the server.

Example:

root@server [~]$ uptime

11:42:52 up 16 days, 8 min, 2 users, load average: 4.91, 5.35, 5.67

From the above example you can find the load and the number of days server running with out failure etc..

Killing process on a server [ kill, pkill, killall -9 ]

kill

This command is used to kill a running process on the server. You need to process id to execute the kill command. Consider you run " pstree -p " which will list all the process with its respective process id. To kill a particular process use the command " kill <process-id> ".

Example:

root@server [~]$ kill 27209

or

root@server [~]$ kill -9 27209

The above command will kill the process id 27209.

pkill

This command will kill the child processes of a particular process. Consider you want kill httpd on the server.

Example:

root@server [~]$ pkill httpd

or

root@server [~]$ pkill -9 httpd

or

root@server [~]$ pkill -HUP httpd

The above command will only kill all the child process of " httpd ". Using this command the parent process will be running and all the child process will be killed.

killall

This command is used to kill all the processes ( parent process and child process ).

Example:

root@server [~]$ killall -9 httpd

root@server [~]$  fuser -k /hsphere/shared/apache2/bin/httpd.prrefork

To Kill ZOMBIE process

root@server [~]$ ps -el | grep 'Z'

The output of the above command will be something like this

F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
4 Z     0   668  4243  0  78   0 -     0 exit   ?        00:09:39 VV <defun>
4 Z     0  1403  4243  0  78   0 -     0 exit   ?        00:08:11 VV <defun>
4 Z     0  1613  4243  0  78   0 -     0 exit   ?        00:09:43 VV <defun>
4 Z     0  2202  4243  0  78   0 -     0 exit   ?        00:09:25 VV <defun>
4 Z     0  2382  4243  0  82   0 -     0 exit   ?        00:08:07 VV <defun>
4 Z     0  2618  4243  0  78   0 -     0 exit   ?        00:09:52 VV <defun>
4 Z     0  2714  4243  0  77   0 -     0 exit   ?        00:09:51 VV <defun>
4 Z     0  2741  4243  0  78   0 -     0 exit   ?        00:09:18 VV <defun>
4 Z     0  2956  4243  0  76   0 -     0 exit   ?        00:07:41 VV <defun>
4 Z     0  3030  4243  0  75   0 -     0 exit   ?        00:00:06 VV <defun>
4 Z     0  3125  4243  0  83   0 -     0 exit   ?        00:08:09 VV <defun>
4 Z     0  3260  4243  0  83   0 -     0 exit   ?        00:09:02 VV <defun>
4 Z     0  3480  4243  0  77   0 -     0 exit   ?        00:09:37 VV <defun>

Checking the number of connection's to the server [ netstat, mysqladmin processlist ]

netstat

This command is used to find the number of connections to the server. " netstat " command will list all the connections using httpd, exim, ftp etc. You can grep the needed port and find the number of connections to a particular port. You can find the Local Address, Foreign Address, State, port etc of all the connections.

Example:

root@server [~]$ netstat -plan

or

root@server [~]$ netstat -plan | grep ":80"

tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 15496/httpd

tcp 0 0 65.254.34.21:80 165.21.14.92:42469 SYN_RECV -

tcp 0 0 65.254.34.21:80 71.7.8.253:3922 SYN_RECV -

tcp 0 0 65.254.34.21:80 165.21.154.10:28343 SYN_RECV -

tcp 0 0 65.254.34.21:80 85.100.25.208:2157 TIME_WAIT -

mysqladmin processlist

This command is used to find the connections to the mysql database. It gives information about Id, User, Host, db, Command, Time, State and Info of a mysql request to the server.

Example:

root@server [~]$ mysqladmin processlist

+--------+-----------------+-----------+-----------------------------+---------+-------+-------+

| Id | User | Host | db | Command | Time | State | Info |

+--------+-----------------+-----------+-----------------------------+---------+-------+-------+

| 186678 | mfjengin_shops | localhost | mfjengin_rapid | Sleep | 28337 | | |

| 188706 | mfjengin_shops | localhost | mfjengin_rapid | Sleep | 27051 | | |

| 195090 | kronosho_usifu | localhost | kroho_sifu | Sleep | 23069 | | |

| 201227 | mfjengin_shops | localhost | mfjengin_rapid | Sleep | 19655 | |

Blocking IP [ apf, csf ]

APF and CSF are firewall software’s.

You can use these commands to block a particular IP from connecting to the server. This command is mainly used when you find too many connections from a particular IP. Normally too many connection might be a attack to the server. So it is important to block such IP before it interrupts the balance of the server.

Check which firewall is installed on your server and use it accordingly.

Example:

root@server [~]$ apf -d <IP>

or

root@server [~]$ csf -d <IP>

Checking the port if open or not [ telnet, nmap ]

telnet

TELNET (TELecommunication NETwork) is a network protocol used on the Internet. TELNET is a client-server protocol, based on a reliable connection-oriented transport. This command will help us to find if a particular port on the server is open or not.

Example:

root@server [~]$ telnet google.com 80

Trying 64.233.187.99...

Connected to google.com (64.233.187.99)

From the above example you could find that port 80 is open on google server. If we receive a " connection refused " signal, that mean's the particular port is not open on the server.

nmap

This command nmap is a Network exploration tool and a security scanner.

root@server [~]$ nmap localhost

Starting Nmap 4.11 ( http://www.insecure.org/nmap/ ) at 2003-06-09 21:55 IST

Interesting ports on localhost.localdomain (127.0.0.1):

Not shown: 1674 closed ports

PORT    STATE SERVICE

21/tcp  open  ftp

22/tcp  open  ssh

25/tcp  open  smtp

111/tcp open  rpcbind

631/tcp open  ipp

734/tcp open  unknown

Nmap finished: 1 IP address (1 host up) scanned in 0.117 seconds

Installing software’s [ yum ]

yum

This command is used to install software’s to the server without any dependences.

Example:

Yum install <software>

If you find any software’s missing on the server, you can directly install it using this yum command. It will install the particular software on the server without dependencies.

fuser -v /hsphere/shared/apache2/bin/httpd.prrefork