When we work on Linux server, the majority of the time we work remotely taking the access to the Linux server and we don’t have the graphical access to the server as a result of which we are operating or managing the Linux server through the command line.
Every Linux Administrator should have the good working understanding of the Linux command line and basic to advance Linux commands. Here in this post, I will let you know, how we can use Linux commands to manage our servers. This will be a series of posts and we will be dividing the command into multiple parts. Below are the commands listed with some of its options and sample output.
This Post Contains the use and explaination of below commands,
- whoami
- users
- who
- w
- echo
- date
- cal
- man
- info
- whatis
So let’s get started.
1. whoami
It shows the name of the user with whom you logged in i.e, to identify your username whoami command is used. Example: if you are logged in as a root user and you use this command, the value returned will be “root“
[root@devopsage ~]# whoami
root
[root@ddevopsage ~]#
2. users
It prints out the Ids of the currently logged in users in your host server.
[root@devopsage ~]# users
sampleuser
[root@devopsage ~]#
3. who
Who command is also used to list out the logged in users like user command does, but only the difference is that who command lists the logged in users along with some detailed format.
It displays,
- Users login name
- login terminal (tty)
- Login date and time.
- Users IP address
[root@devopsage ~]# who
sampleuser1 pts/0 2018-02-24 07:58 (157.48.246.125)
sampleuser2 pts/1 2018-02-24 08:13 (localhost)
Here, the 1st column shows the username, the 2nd column shows their terminal, the 3rd column shows date, the 4th column shows time and the 5th column shows the machine Ip address from where they are logged in.
Options:
- -H: prints the column header
- -u: Will print with some more details like PID and IDLE time.
- -b: this options indicate the time and date of the last reboot
4. w
This command will also show the logged in user along with what users are doing. Linux keeps a track of which users are logged in and what they are doing at that time. w commands list out the logged in users and also displays what processes they are running.
[root@devopsage ~]# w
08:32:19 up 1:06, 2 users, load average: 0.00, 0.01, 0.05
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
sampleuser1 pts/0 157.48.246.125 07:58 8:43 0.05s 0.18s sshd: sampleuser1 [priv]
sampleuser2 pts/3 localhost 08:36 4.00s 0.00s 0.00s ping localhost
[root@devopsage ~]#
5. echo
echo command is used to print the output of any message on the screen it is also used to print the value of certain variables.
[root@devopsage ~]# echo "welcome to devopsage"
welcome to devopsage
[root@devopsage ~]# echo $HOME
/root
[root@devopsage ~]#
6. date
date command is used to display the date and time of the server. It is also used to set the date on the server
[root@devopsage ~]# date
Sat Feb 24 08:48:08 UTC 2018
[root@devopsage ~]#
Options:
- %m: month of the year (01-12)
- %d: day of the month (01-31)
- %y: last two digits of the year (00-99)
- %D: date as mm/dd/yy format
- %n: displays output at new line
- %S: second (0-59)
- %M: minute (0-59)
- %H: hour (0-23)
- %T: time as HH:MM:SS
- %j: day of year (001-365)
- %w: day of the week (0-6) //0 is sunday
- %a: weekdays (sun-sat)
- %h: month (jan-dec)
- %r: 12 hour time format. ex: 09:00:03 AM
[root@devopsage ~]# date
Sat Feb 24 09:05:47 UTC 2018
[root@devopsage ~]# date '+%m/%d/%y %H:%M:%S'
02/24/18 09:05:49
[root@devopsage ~]# date '+%m/%d/%y %n%H:%M:%S'
02/24/18
09:06:07
[root@devopsage ~]#
7. cal
cal command displays the calendar for the current month. It can also display entire year calendar for the mentioned year or a single month calendar for the mentioned month and year.
Options:
- -j: Displays Julian dates (1-365), starting from 1st January
- -m: Display Monday as the first day of the week
- -y: Display whole year
- -v: Display calendar source.
[root@devopsage ~]# cal
February 2018
Su Mo Tu We Th Fr Sa
1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28
[root@devopsage ~]# cal 1 2018
January 2018
Su Mo Tu We Th Fr Sa
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31
[root@devopsage ~]# cal 2018
2018
January February March
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 5 6 1 2 3 1 2 3
7 8 9 10 11 12 13 4 5 6 7 8 9 10 4 5 6 7 8 9 10
14 15 16 17 18 19 20 11 12 13 14 15 16 17 11 12 13 14 15 16 17
21 22 23 24 25 26 27 18 19 20 21 22 23 24 18 19 20 21 22 23 24
28 29 30 31 25 26 27 28 25 26 27 28 29 30 31
April May June
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 5 6 7 1 2 3 4 5 1 2
8 9 10 11 12 13 14 6 7 8 9 10 11 12 3 4 5 6 7 8 9
15 16 17 18 19 20 21 13 14 15 16 17 18 19 10 11 12 13 14 15 16
22 23 24 25 26 27 28 20 21 22 23 24 25 26 17 18 19 20 21 22 23
29 30 27 28 29 30 31 24 25 26 27 28 29 30
July August September
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 5 6 7 1 2 3 4 1
8 9 10 11 12 13 14 5 6 7 8 9 10 11 2 3 4 5 6 7 8
15 16 17 18 19 20 21 12 13 14 15 16 17 18 9 10 11 12 13 14 15
22 23 24 25 26 27 28 19 20 21 22 23 24 25 16 17 18 19 20 21 22
29 30 31 26 27 28 29 30 31 23 24 25 26 27 28 29
30
October November December
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 2 3 4 5 6 1 2 3 1
7 8 9 10 11 12 13 4 5 6 7 8 9 10 2 3 4 5 6 7 8
14 15 16 17 18 19 20 11 12 13 14 15 16 17 9 10 11 12 13 14 15
21 22 23 24 25 26 27 18 19 20 21 22 23 24 16 17 18 19 20 21 22
28 29 30 31 25 26 27 28 29 30 23 24 25 26 27 28 29
30 31
[root@devopsage ~]#
8. man
This command shows the manual of the command. It is often called as manual pages or simply man pages. It gives you a complete information of the command, with all its details, options etc.
Example: man cal , it will give you every details of the cal command. Output of man command is a complete file with organised details of that perticular command.
[root@devopsage ~]# man cal // manual for the cal command
9. info
info command is similar to the man command, it also gives some information about the command passed as an arguments.
[root@devopsage ~]# info cal
10. whatis
This command will give you short information about the command used as an argument
Example:
[root@devopsage ~]# whatis cal
cal (1) - display a calendar
[root@devopsage ~]#