Introduction to Linux. Lesson 11. 50 Most Frequently Used Linux Commands. Part 2.
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Some of those commands , you already know from previous lessons. You have opportunity to repeat to cement your knowledge.
Use kill command to terminate a process. First get the process id using ps -ef command, then use kill -9 to kill the running Linux process as shown below. You can also use killall, pkill, xkill to terminate a unix process. $ ps -ef | grep vim ramesh 7243 7222 9 22:43 pts/2 00:00:00 vim
$ kill -9 7243 More kill examples: 4 Ways to Kill a Process – kill, killall, pkill, xkill 27. rm command examples Get confirmation before removing the file. $ rm -i filename.txt It is very useful while giving shell metacharacters in the file name argument. Print the filename and get confirmation before removing the file. $ rm -i file* Following example recursively removes all files and directories under the example directory. This also removes the example directory itself. $ rm -r example 28. cp command examples Copy file1 to file2 preserving the mode, ownership and timestamp. $ cp -p file1 file2 Copy file1 to file2. if file2 exists prompt for confirmation before overwritting it. $ cp -i file1 file2 29. mv command examples Rename file1 to file2. if file2 exists prompt for confirmation before overwritting it. $ mv -i file1 file2 Note: mv -f is just the opposite, which will overwrite file2 without prompting. mv -v will print what is happening during file rename, which is useful while specifying shell metacharacters in the file name argument. $ mv -v file1 file2 30. cat command examples You can view multiple files at the same time. Following example prints the content of file1 followed by file2 to stdout. $ cat file1 file2 While displaying the file, following cat -n command will prepend the line number to each line of the output. $ cat -n /etc/logrotate.conf 1 /var/log/btmp { 2 missingok 3 monthly 4 create 0660 root utmp 5 rotate 1 6 } 31. mount command examples To mount a file system, you should first create a directory and mount it as shown below.
You can also add this to the fstab for automatic mounting. i.e Anytime system is restarted, the filesystem will be mounted.
/dev/sdb1 /u01 ext2 defaults 0 2
32. chmod command examples
chmod command is used to change the permissions for a file or directory.
Give full access to user and group (i.e read, write and execute ) on a specific file.
$ chmod ug+rwx file.txt
Revoke all access for the group (i.e read, write and execute ) on a specific file.
$ chmod g-rwx file.txt
Apply the file permissions recursively to all the files in the sub-directories.
$ chmod -R ug+rwx file.txt
More chmod examples: 7 Chmod Command Examples for Beginners
33. chown command examples
chown command is used to change the owner and group of a file.
To change owner to oracle and group to db on a file. i.e Change both owner and group at the same time.
$ chown oracle:dba dbora.sh
Use -R to change the ownership recursively.
$ chown -R oracle:dba /home/oracle
34. passwd command examples
Change your password from command line using passwd. This will prompt for the old password followed by the new password.
$ passwd
Super user can use passwd command to reset others password. This will not prompt for current password of the user.
Remove password for a specific user. Root user can disable password for a specific user. Once the password is disabled, the user can login without entering the password.
$ ifconfig eth0 down More ifconfig examples: Ifconfig: 7 Examples To Configure Network Interface 37. uname command examples Uname command displays important information about the system such as — Kernel name, Host name, Kernel release number, Processor type, etc., Sample uname output from a Ubuntu laptop is shown below. $ uname -a Linux john-laptop 2.6.32-24-generic #41-Ubuntu SMP Thu Aug 19 01:12:52 UTC 2010 i686 GNU/Linux 38. whereis command examples When you want to find out where a specific Unix command exists (for example, where does ls command exists?), you can execute the following command. $ whereis ls ls: /bin/ls /usr/share/man/man1/ls.1.gz /usr/share/man/man1p/ls.1p.gz When you want to search an executable from a path other than the whereis default path, you can use -B option and give path as argument to it. This searches for the executable lsmk in the /tmp directory, and displays it, if it is available. $ whereis -u -B /tmp -f lsmk lsmk: /tmp/lsmk 39. whatis command examples Whatis command displays a single line description about a command. $ whatis ls ls (1) - list directory contents
$ whatis ifconfig ifconfig (8) - configure a network interface 40. locate command examples Using locate command you can quickly search for the location of a specific file (or group of files). Locate command uses the database created by updatedb. The example below shows all files in the system that contains the word crontab in it. $ locate crontab /etc/anacrontab /etc/crontab /usr/bin/crontab /usr/share/doc/cron/examples/crontab2english.pl.gz /usr/share/man/man1/crontab.1.gz /usr/share/man/man5/anacrontab.5.gz /usr/share/man/man5/crontab.5.gz /usr/share/vim/vim72/syntax/crontab.vim 41. man command examples Display the man page of a specific command. $ man crontab When a man page for a command is located under more than one section, you can view the man page for that command from a specific section as shown below. $ man SECTION-NUMBER commandname Following 8 sections are available in the man page.
$ man 5 crontab 42. tail command examples Print the last 10 lines of a file by default. $ tail filename.txt Print N number of lines from the file named filename.txt $ tail -n N filename.txt View the content of the file in real time using tail -f. This is useful to view the log files, that keeps growing. The command can be terminated using CTRL-C. $ tail -f log-file More tail examples: 3 Methods To View tail -f output of Multiple Log Files in One Terminal 43. less command examples less is very efficient while viewing huge log files, as it doesn’t need to load the full file while opening. $ less huge-log-file.log One you open a file using less command, following two keys are very helpful. CTRL+F – forward one window CTRL+B – backward one window More less examples: Unix Less Command: 10 Tips for Effective Navigation 44. su command examples Switch to a different user account using su command. Super user can switch to any other user without entering their password. $ su - USERNAME Execute a single command from a different account name. In the following example, john can execute the ls command as raj username. Once the command is executed, it will come back to john’s account. [john@dev-server]$ su - raj -c 'ls'
[john@dev-server]$ Login to a specified user account, and execute the specified shell instead of the default shell. $ su -s 'SHELLNAME' USERNAME 45. mysql command examples mysql is probably the most widely used open source database on Linux. Even if you don’t run a mysql database on your server, you might end-up using the mysql command ( client ) to connect to a mysql database running on the remote server. To connect to a remote mysql database. This will prompt for a password. $ mysql -u root -p -h 192.168.1.2 To connect to a local mysql database. $ mysql -u root -p If you want to specify the mysql root password in the command line itself, enter it immediately after -p (without any space). 46. yum command examples To install apache using yum. $ yum install httpd To upgrade apache using yum. $ yum update httpd To uninstall/remove apache using yum. $ yum remove httpd 47. rpm command examples To install apache using rpm.
To upgrade apache using rpm.
To uninstall/remove apache using rpm.
More rpm examples: RPM Command: 15 Examples to Install, Uninstall, Upgrade, Query RPM Packages 48. ping command examples Ping a remote host by sending only 5 packets. $ ping -c 5 gmail.com More ping examples: Ping Tutorial: 15 Effective Ping Command Examples 49. date command examples Set the system date:
Once you’ve changed the system date, you should syncronize the hardware clock with the system date as shown below.
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