Linuxcommands

Linux Commands

$ ls -las # list directory contents

$ touch aa.txt ## create an empty file

$ mv aa.txt bb.txt # rename file

$ rm -i aa.txt # confirm and remove file

$ rm -r example 

$ mkdir # make directory

$ cd /home/user # absolute path

$ cd test/ # relative path

chown and chmod

$ chown user:group demo.txt

example is chown john:users demo.txt

chmod command samples

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

$ chmod 400 aa.txt

$ chmod +x aa.txt

tar command samples

$ tar cvf archive_name.tar dirname/

$ tar xvf archive_name.tar

grep command samples

$ grep -i “the” demo_file Search for a given string in a file (case in-sensitive search).

$ grep -A 3 -i “example” demo_text Print the matched line, along with the 3 lines after it.

$ grep -r “bread” * Search for a given string in all files recursively

find command samples

$ find -iname “notes.txt”

Execute commands on files found by the find command

$ find -iname “notes.txt” -exec md5sum {} ;

Find all empty files in home directory

$ find ~ -empty

sed command samples

This example converts the DOS file format to Unix file format using sed command.

sed′s/.//’ filename

Print file content in reverse order

$ sed -n ‘1!G;h;$p’ thegeekstuff.txt

Add line number for all non-empty-lines in a file

$ sed ‘/./=’ thegeekstuff.txt | sed ‘N; s// /’

awk command samples

Remove duplicate lines using awk

$ awk ‘!($0 in array) { array[$0]; print }’ temp

Print all lines from /etc/passwd that has the same uid and gid

$awk -F ‘:’ ‘$3==$4’ passwd.txt

Print only specific field from a file.

$ awk ‘{print $2,$5;}’ employee.txt

service command samples

$ service ssh status

$ service --status-all

$ service ssh restart

top command samples

$ top

$ top -u testuser

Cron command samples

View crontab entry for a specific user

$ crontab -u john -l

Schedule a cron job every 10 minutes.

/10 * * * /home/john/check-disk-space

This will execute the Full backup shell script (full-backup) on 10th June 08:30 AM.

Please note that the time field uses 24 hours format. So, for 8 AM use 8, and for 8 PM use 20.

30 08 10 06 * /home/john/full-backup

00 11,16 * * * /home/ramesh/bin/incremental-backup

00 – 0th Minute (Top of the hour) 11,16 – 11 AM and 4 PM * – Every day * – Every month * – Every day of the week

9 to 6 pm every week day

00 09-18 * * * /home/john/bin/check-db-status

9 to 6 pm Monday to Friday

00 09-18 * * 1-5 /home/ramesh/john/check-db-status

$ crontab -l # list crontab entries

$ crontab -e # edit crontab entries

MySql command samples

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

Yum command samples

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

rpm command samples

To install apache using rpm.

$ rpm -ivh httpd-2.2.3-22.0.1.el5.i386.rpm

To upgrade apache using rpm

$ rpm -uvh httpd-2.2.3-22.0.1.el5.i386.rpm

To uninstall/remove apache using rpm

$ rpm -ev httpd

apt command samples

$ apt update

$ apt install packagename

$ apt remove packagename

Other Commands

$ df
$ free 
$ kill
$ ps
$ whereis
$ which python
$ whatis ls
$ locate crontab
$ tail /var/log/nginx/access.log
$ less /var/log/nginx/error.log
$ ping
$ date
$ wget 
$ curl

echo 'foo' | tee foo.txt
foo
cat foo.txt
foo