The most practical 30 Linux commands!

This article describes some useful and common Linux or UNIX commands that are commonly used by Linux system administrators. Instead of a complete list, this article briefly lists the commands that come in handy when needed, starting with an example of how to use these commands.

1.uptime command

In Linux, the uptime command shows how long your system has been running and how many users are currently logged on, plus a load average of 1 minutes, 5 minutes, and 15 minutes.

# uptime 08:16:26 up min, 1 user,  load average:0.00, 0.03, 0.22

Check the uptime version

In addition to uptime (uptime) and version (versions), the Uptime command has no other options. If the time is less than 1 days, it only gives information hours:mins this form.

[Email protected] ~]$ uptime-v Procps version 3.2.8

2.w command

This command displays the currently logged on user and their processes, plus the load average. In addition, it shows the login name, TTY name, remote host, logon time, idle time, JCPU, PCPU, commands, and processes.

available Options- H: Does not display the caption. -S: jcpu and PCPU are not displayed. -F: Field information is not displayed. -V: (uppercase V)-Displays the version.

3.users Command

The users command shows the currently logged-on user, which has no additional parameters other than help and version.

# users Tecmint

4.who Command

The WHO command returns only the user name, date, time, and host information; The WHO command is similar to the W command, unlike the W command, who does not export the information that the user performs, it may be useful to look at the difference between the two commands of WHO and W.

# who tecmint pts/0 2010-09-18 07:59 (192.168.50.1)

The WHO command option- B: Displays the last system restart date and time. -R: Displays the current runlevel. -a,–all: Displays all accumulated information.

5.whoami Command

The WhoAmI command outputs the current user's name; You can also use the "Who am I" command to display the current user, if you log in as root user using the sudo command, the "WhoAmI" command returns the root user is the current user, if you want to know specifically which user is logged in, use "Who Am I" Command.

# WhoAmI Tecmint

6.ls Command

The LS command displays a list of files in human readable format.

# ls-l Total dr-xr-xr-x.   2 root root 4096 Sep 08:46 bin Dr-xr-xr-x. 5 root root Sep 8 15:49 boot

Sorts the files according to the last modification time.

# ls-ltr Total 40-rw-r--r--. 1 root root 6546 Sep 18:42 install.log.syslog-rw-r--r--. 1 root root 22435 Sep 18:45 install.log-rw-------. 1 root root 1003 Sep 18:45 anaconda-ks.cfg

7.crontab Command

You can use the crontab command and the-l option to list the current user's scheduled tasks.

# crontab-l * * */bin/ls >/ls.txt

You can use the-e option to edit crontab, in the following example, you will use the VI Editing tool to open the scheduled task, make the necessary changes, press: Wq key to exit, this will automatically save the settings.

# CRONTAB-E

8.less Command

The less command allows you to quickly view the file; You can page up and down, press "Q" to exit the less window.

# less Install.log installing Setup-2.8.14-10.el6.noarch warning:setup-2.8.14-10.el6.noarch:header V3 RSA/SHA256 Signature, key ID C105b9de:nokey installing filesystem-2.4.30-2.1.el6.i686 installing Ca-certificates-2010.63-3.el6.noarch Installing Xml-common-0.6.3-32.el6.noarch nstalling tzdata-2010l-1.el6.noarch Installing Iso-codes-3.16-2.el6.noarch

9.more Command

The more command allows you to quickly view the file and display details as a percentage, you can page up and down, press "Q" to exit the more window.

# more Install.log installing Setup-2.8.14-10.el6.noarch warning:setup-2.8.14-10.el6.noarch:header V3 RSA/SHA256 Signature, key ID C105b9de:nokey installing filesystem-2.4.30-2.1.el6.i686 installing Ca-certificates-2010.63-3.el6.noarch Installing Xml-common-0.6.3-32.el6.noarch Installing Tzdata-2010l-1.el6.noarch Installing Iso-codes-3.16-2.el6.noarch--more--(10%)

10.CP Command

Copies files from the source to the destination, preserving the same pattern.

# cp-p FileA Fileb

The system will prompt you before overwriting the file.

# cp-i FileA Fileb

11.MV Command

Rename Filea to Fileb; the-i option will prompt before overwriting, and if the file already exists, it will be required to be confirmed.

# mv-i FileA Fileb

12.cat Command

The cat command is used to view multiple files simultaneously.

# Cat FileA Fileb

If a file cannot be displayed on a screen/page, you can use the Cat command to combine the more and less commands to view the contents of the file.

# Cat Install.log | Less      or# cat Install.log |

13.cd command (switch directory)

With the CD command (switch directory), it goes to the Filea directory.

# Cd/filea

14.pwd command (output working directory)

The PWD command returns the current working directory.

# Pwd/root

15.sort Command

Sorts a row of text files in ascending order, and if you use the-r option, it is sorted in descending order.

#sort Filea.txt#sort-r FileA.txt

16.VI Command

For most Unix-like operating systems, VI is the most popular text editor, the following example uses the-r option, open a read-only file, press ": Q" to exit the VI window.

# Vi-r/etc/shadows

17.ssh command (Secure Shell)

The SSH command is used to log in to the remote host, for example, the following SSH example uses the user as a narad to connect to the host (192.168.50.2).

# SSH [email protected]

To check the version of SSH, use the option-V (uppercase) to display the version of SSH.

# SSH-VOPENSSH_5.3P1, OpenSSL 1.0.0-fips 2010

18.ftp or SFTP Command

FTP or SFTP commands are used to connect to remote FTP hosts, FTP refers to file transfer protocols, and SFTP is a secure file transfer protocol. For example, the following command will connect to the FTP host (192.168.50.2).

# FTP 192.168.50.2# sftp 192.168.50.2

Just as you can use Mput to upload multiple files to a remote host, we can also use Mget to download multiple files from a remote host.

# FTP > Mput *.txt# ftp > Mget *.txt

19.service Command

The service command invokes the script located at the/etc/init.d/directory and executes the script. There are two ways to start any service, for example, we use the service command to start the services named httpd.

# service httpd start#/etc/init.d/httpd start

20.free Command

The free command displays information about idle memory, total memory, and intra-swap, in bytes.

# free Total used  free shared buffers cached mem:1030800 735944 29 4856 0 51648 547696-/+ buffers/cache:136600 894200 swap:2064376 0 2064376

The free command with the-t option shows the total memory used and the memory that can be used, in bytes.

# free-t Total used free shared buffers cached mem:1030800 736096 294704 0 51720 547704-/+ buffers/cache:136672 894128 swap:2064376 0 2064376 total:30951 76 736096 2359080

21.top Command

The top command shows the processor activity of the system, and also shows the tasks managed by the kernel in real time, which shows the processor and memory used, and if you use the top command with the "u" option, this displays the specific user process details, as follows: Press "O" (uppercase) to sort the way you want, press "Q" To exit the top screen.

# top-u TecmintTop-11:13:11 up 3:19, 2 users,Load average:0.00, 0.00, 0.00 tasks:116 Total, 1 running, sleeping, 0 stopped, 0 zombie Cpu (s): 0.0%us, 0.3% Sy, 0.0%ni, 99.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st mem:1030800k Total, 736188k used, 294612kFree, 51760k buffers swap:2064376k total, 0k used, 2064376kfree,   547704k cached pid user       pr  ni  virt  res  shr s %cpu % Mem    time+  command 1889 tecmint   20    0 11468 1648  920 S  0.0  0.2    0:00.59 sshd 1890 tecmint   20   0  5124 1668 1416  s  0.0  0.2   0:00.44 bash 6698 tecmint   20    0 11600 1668  924 S  0.0  0.2    0:01.19 sshd 6699 tecmint   20   0  5124 1596 1352  s  0.0  0.2   0:00.11 bash   

22.tar Command

The tar command is used to compress files and folders under Linux; For example, the following command creates a compressed archive for the/home directory with the file name Archive-name.tar.

# TAR-CVF Archive-name.tar/home

To extract the Tar compressed archive file, use the options shown below.

# TAR-XVF Archive-name.tar

23.grep Command

grep searches for a specific string in the file; only the Tecmint user in the/etc/passwd file is displayed. We can use the-I option, ignoring case.

# grep TECMINT/ETC/PASSWD Tecmint:x:500:500::/home/tecmint:/bin/bash

24.find Command

The Find command searches for files, strings, and directories; In the following example, the Find command searches for the tecmint word in the "/" partition and returns the output.

# Find/-name Tecmint/var/spool/mail/tecmint/home/tecmint/root/home/tecmint

25.lsof Command

Lsof means "list all open files"; below, the lsof command lists all files opened by tecmint users.

# lsof-u Tecmint  COMMAND  PID    USER   FD   TYPE     DEVICE size/off   NODE NAME   sshd    1889 Tecmint  cwd    DIR      253,0     4096      2/   sshd    1889 tecmint  txt    REG      253,0   532336 298069/usr/sbin/sshd   sshd    1889 tecmint  DEL    REG      253,0          412940/lib/ libcom_err.so.2.1   sshd    1889 tecmint  DEL    REG      253,0          393156/lib/ld-2.12.so   sshd    1889 Tecmint  Del    reg      253,0          298643/usr/lib/libcrypto.so.1.0.0   sshd    1889 tecmint  DEL    reg      253,0          393173/lib/libnsl-2.12.so   sshd    1889 tecmint  DEL    REG      253,0          412937 /lib/libkrb5support.so.0.1   sshd    1889 tecmint  DEL    REG      253,0          412961/lib/libplc4.so

26.last Command

With the last command, we can observe the activity of the user in the system, which can also be performed as a normal user, which displays complete user information, such as terminal, time, date, system restart or boot, and kernel version, which is a useful command for troubleshooting.

# last  tecmint  pts/1        192.168.50.1     Tue Sep 08:50 still logged in   tecmint  pts/0        192.168.50.1     Tue Sep 07:59   still logged in   reboot   system boot  2.6.32-279.el6.i Tue Sep 18 07:54-11:38  (03:43)   root     pts/1        192.168.50.1     Sun Sep 10:40-down   (03:53)   root     pts/0        : 0.0             Sun Sep 10:36-13:09  (02:32)   root     tty1         : 0               Sun Sep 16 10:07- Down   (04:26)   reboot   system boot  2.6.32-279.el6.i Sun Sep 09:57-14:33  (04:35)   Narad    pts/2        192.168.50.1     Thu Sep 08:07-down   

You can use the last with the user name to understand the activity of a specific user, as shown below.

# last Tecmint  tecmint  pts/1        192.168.50.1     Tue Sep-08:50 still   logged in   tecmint  pts/0        192.168.50.1     Tue Sep 07:59   still logged in   tecmint  pts/1        192.168.50.1     Thu Sep 08:07-down   (01:15)   tecmint  pts/4        192.168.50.1     Wed Sep 12 10:12-12:29  

27.ps Command

The PS command displays information about the processes running in the system, and the following example shows only the init process.

# Ps-ef |        grep init root 1 0 0 07:53? 00:00:04/sbin/init root 7508 6825 0 11:48 pts/1 00:00:00 grep init

28.kill Command

Use the KILL command to end the process; Use the PS command to find the process ID, as shown below, and then use the kill-9 command to terminate the process.

# Ps-ef |        grep init root 1 0 0 07:53? 00:00:04/sbin/init root 7508 6825 0 11:48 pts/1 00:00:00 grep init# kill-9 7508

29.rm Command

The RM command is used to purge or delete files without prompting for confirmation.

# RM FileName

Use the-I option to confirm the deletion before deleting it, and use the "-R" and "-f" options to forcibly delete the file without confirming it.

# rm-i test.txtrm:remove regular file ' Test.txt '?

30.mkdir Command

The mkdir command is used to create directories under Linux.

# mkdir DirectoryName

This is similar to Linux/unix operating system under a series of easy-to-use, and very practical daily basic commands, if we miss out what orders, welcome message exchange!

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The most practical 30 Linux commands!