Linux commands for beginners part 2

Linux commands for beginners part 2

Hi welcome to second part of Linux commands for beginners .If you are feeling comfortable with Linux commands you can surely easily understand the File Hierarchy System of Linux. Let’s start with commands which are very useful for any linux Administrator.

We will start with very powerful command which is Pipe represented by sign (|). Basically it is used for redirect the output of one command into another command. Syntax command1 | command2.
See the practical example of pipe(|) in below screenshot. First command is creating list of directory. Then output is piped and its counting number of line of output which is 11.

In second command we are piping output of directory listing and displaying first 5 lines of listing.

[fahmed@faraz var]# ls -l | wc -l
24

[fahmed@faraz var]# ls -l | head -5
total 88
drwxr-xr-x. 2 root root 4096 Oct 30 2014 account
drwxr-xr-x. 15 root root 4096 Nov 5 2014 cache
drwxr-xr-x. 2 root root 4096 Oct 30 2014 crash
drwxr-xr-x. 2 root root 4096 Feb 2 2012 cvs

Now another kool command . I am going to change lower case letters to upper case letters in file and vice versa.

Syntax tr ‘a-z’ ‘A-Z’ < file-name. See the below image;

If you want to switch user then use su command

If you just type su and hit enter then it automatically switch to root.

If you have an ordinary user then type user-name.

Syntax su user-name.

To view and change the host/machine name we can use command hostname.

Syntax hostname new-hostname. (Note: you must be on root privilege.)

free command is used to view the memory status.

Syntax free [option].
Useful options are free –l (show the memory with detail),
free –m (show the memory with Mbs),
free –g (show the memory with Gbs).

[fahmed@faraz var]# free
             total       used       free     shared    buffers     cached
Mem:      22540264    2007488   20532776          0     234092     573932
-/+ buffers/cache:    1199464   21340800
Swap:     11530232          0   11530232
[fahmed@faraz var]# free -l
             total       used       free     shared    buffers     cached
Mem:      22540264    2007620   20532644          0     234096     573928
Low:      22540264    2007620   20532644
High:            0          0          0
-/+ buffers/cache:    1199596   21340668
Swap:     11530232          0   11530232
[fahmed@faraz var]# free -m
             total       used       free     shared    buffers     cached
Mem:         22011       1960      20051          0        228        560
-/+ buffers/cache:       1171      20840
Swap:        11259          0      11259
[fahmed@faraz var]# free -g
             total       used       free     shared    buffers     cached
Mem:            21          1         19          0          0          0
-/+ buffers/cache:          1         20
Swap:           10          0         10

du command is used to view the used disk space by any directory.

Syntax du dir-name.
Useful options are du –c (show the grand total),
du –h (human readable form),
du –s (show only a total size).