0 0
Read Time:21 Minute, 23 Second

Hello Guys Welcome Back to Linuxtips. My Name is Manikantasripadi.

If your application isn’t working—or you’re just looking for more information—these 20 commands will come in handy.

1. Command: ifconfig

ifconfig is used to configure the kernel-resident network interfaces. It is used at boot time to set up interfaces as necessary. After that, it is usually only needed when debugging or when system tuning is needed.

Check Active Network Interfaces

[manikantasripadi@linuxtips ~]$ ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 9001
        inet 172.31.42.130  netmask 255.255.240.0  broadcast 172.31.47.255
        inet6 fe80::22:e2ff:fe6a:1a40  prefixlen 64  scopeid 0x20<link>
        ether 02:22:e2:6a:1a:40  txqueuelen 1000  (Ethernet)
        RX packets 2429578  bytes 862420803 (822.4 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 1925257  bytes 2925041730 (2.7 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 1762032  bytes 761931267 (726.6 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 1762032  bytes 761931267 (726.6 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[manikantasripadi@linuxtips ~]$ 

Check All Network Interfaces

Display details of All interfaces including disabled interfaces using “-a” argument.

[manikantasripadi@linuxtips ~]$  ifconfig -a
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 9001
        inet 172.31.42.130  netmask 255.255.240.0  broadcast 172.31.47.255
        inet6 fe80::22:e2ff:fe6a:1a40  prefixlen 64  scopeid 0x20<link>
        ether 02:22:e2:6a:1a:40  txqueuelen 1000  (Ethernet)
        RX packets 2433681  bytes 862886184 (822.9 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 1928897  bytes 2933574615 (2.7 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 1765783  bytes 763441756 (728.0 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 1765783  bytes 763441756 (728.0 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[manikantasripadi@linuxtips ~]$ 

Disable an Interface

[manikantasripadi@linuxtips ~]$  ifconfig eth0 down

Enable an Interface

[manikantasripadi@linuxtips ~]$  ifconfig eth0 up

Assign IP Address to an Interface

Assign “172.31.42.136” as the IP address for the interface eth0.

[manikantasripadi@linuxtips ~]$ ifconfig eth0 192.168.1.12

Change Subnet Mask of Interface eth0

[manikantasripadi@linuxtips ~]$ ifconfig eth0 netmask 255.255.255.

Change Broadcast Address of Interface eth0

[manikantasripadi@linuxtips ~]$ ifconfig eth0 broadcast 192.168.1.255

Assign IP Address, Netmask and Broadcast to Interface eth0

[manikantasripadi@linuxtips ~]$ ifconfig eth0 192.168.1.12 netmask 255.255.255.0 broadcast 192.168.1.255

Note: If using a wireless network you need to use command “iwconfig“. For more “ifconfig” command

2. Command: netstat

netstat command displays various network related information such as network connections, routing tables, interface statistics, masquerade connections, multicast memberships etc..,

List All Network Ports

[manikantasripadi@linuxtips ~]$ netstat -a

Active UNIX domain sockets (servers and established)
Proto RefCnt Flags       Type       State         I-Node   Path
unix  2      [ ACC ]     STREAM     LISTENING     741379   /run/user/user1/keyring-I5cn1c/gpg
unix  2      [ ACC ]     STREAM     LISTENING     8965     /var/run/acpid.socket
unix  2      [ ACC ]     STREAM     LISTENING     18584    /tmp/.X11-unix/X0
unix  2      [ ACC ]     STREAM     LISTENING     741385   /run/user/user1/keyring-I5cn1c/ssh
unix  2      [ ACC ]     STREAM     LISTENING     741387   /run/user/user1/keyring-I5cn1c/pkcs11
unix  2      [ ACC ]     STREAM     LISTENING     20242    @/tmp/dbus-ghtTjuPN46
unix  2      [ ACC ]     STREAM     LISTENING     13332    /var/run/samba/winbindd_privileged/pipe
unix  2      [ ACC ]     STREAM     LISTENING     13331    /tmp/.winbindd/pipe
unix  2      [ ACC ]     STREAM     LISTENING     11030    /var/run/mysqld/mysqld.sock
unix  2      [ ACC ]     STREAM     LISTENING     19308    /tmp/ssh-qnZadSgJAbqd/agent.3221
unix  2      [ ACC ]     STREAM     LISTENING     436781   /tmp/HotShots
unix  2      [ ACC ]     STREAM     LISTENING     46110    /run/user/ravisaive/pulse/native
unix  2      [ ACC ]     STREAM     LISTENING     19310    /tmp/gpg-zfE9YT/S.gpg-agent
...

List All TCP Ports

[manikantasripadi@linuxtips ~]$ netstat -at

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State      
tcp        0      0 localhost:mysql         *:*                     LISTEN     
tcp        0      0 *:5901                  *:*                     LISTEN     
tcp        0      0 *:5902                  *:*                     LISTEN     
tcp        0      0 *:x11-1                 *:*                     LISTEN     
tcp        0      0 *:x11-2                 *:*                     LISTEN     
tcp        0      0 *:5938                  *:*                     LISTEN     
tcp        0      0 localhost:5940          *:*                     LISTEN     
tcp        0      0 ravisaive-OptiPl:domain *:*                     LISTEN     
tcp        0      0 ravisaive-OptiPl:domain *:*                     LISTEN     
tcp        0      0 localhost:ipp           *:*                     LISTEN     
tcp        0      0 ravisaive-OptiPle:48270 ec2-23-21-236-70.c:http ESTABLISHED
tcp        0      0 ravisaive-OptiPle:48272 ec2-23-21-236-70.c:http TIME_WAIT  
tcp        0      0 ravisaive-OptiPle:48421 bom03s01-in-f22.1:https ESTABLISHED
tcp        0      0 ravisaive-OptiPle:48269 ec2-23-21-236-70.c:http ESTABLISHED
tcp        0      0 ravisaive-OptiPle:39084 channel-ecmp-06-f:https ESTABLISHED
...

Show Statistics for All Ports

[manikantasripadi@linuxtips ~]$ netstat -s

Ip:
    4994239 total packets received
    0 forwarded
    0 incoming packets discarded
    4165741 incoming packets delivered
    3248924 requests sent out
    8 outgoing packets dropped
Icmp:
    29460 ICMP messages received
    566 input ICMP message failed.
    ICMP input histogram:
        destination unreachable: 98
        redirects: 29362
    2918 ICMP messages sent
    0 ICMP messages failed
    ICMP output histogram:
        destination unreachable: 2918
IcmpMsg:
        InType3: 98
        InType5: 29362
        OutType3: 2918
Tcp:
    94533 active connections openings
    23 passive connection openings
    5870 failed connection attempts
    7194 connection resets received
....

OK! For some reason if you want not to resolve host, port and user name as a output of netstat.

[manikantasripadi@linuxtips ~]$ netstat -an

Fine, you may need to get the output of netstat continuously till interrupt instruction is passed (ctrl+c).

[manikantasripadi@linuxtips ~]$ netstat -c

3. Command: nslookup

A network utility program used to obtain information about Internet servers. As its name suggests, the utility finds name server information for domains by querying DNS.

[manikantasripadi@linuxtips ~]$ nslookup linuxtips.in 

Server:		172.31.42.130
Address:	172.31.42.130#53 

Non-authoritative answer: 
Name:	linuxtips.in 
Address: 202.65.142.76

Query Mail Exchanger Record

[manikantasripadi@linuxtips ~]$ nslookup -query=mx linuxtips.in 

Server:		172.31.42.130 
Address:	172.31.42.130#53 

Non-authoritative answer: 
linuxtips.in	mail exchanger = 0 mail.neoistone.com. 
linuxtips.in	mail exchanger = 10 mail.neoistone.com. 

Authoritative answers can be found from:

Query Name Server

[manikantasripadi@linuxtips ~]$ nslookup -type=ns linuxtips.in 

Server:		172.31.42.130 
Address:	172.31.42.130#53 

Non-authoritative answer: 
linuxtips.in	nameserver = ns1.neoistone.com. 
linuxtips.in	nameserver = ns1.neoistone.com. 

Authoritative answers can be found from:

Query DNS Record

[manikantasripadi@linuxtips ~]$ nslookup -type=any linuxtips.in

Server:		172.31.42.130 
Address:	172.31.42.130#53 

Non-authoritative answer: 
linuxtips.in	mail exchanger = 10 mail.neoistone.com. 
linuxtips.in	mail exchanger = 0  mail.neoistone.com. 
linuxtips.in	nameserver = ns1.neoistone.com. 
linuxtips.in	nameserver = ns2.neoistone.com.  

Authoritative answers can be found from:

Query Start of Authority

[manikantasripadi@linuxtips ~]$ nslookup -type=soa linuxtips.in

Server:		172.31.42.130
Address:	172.31.42.130#53

Non-authoritative answer:
linuxtips.in
	origin = ns1.neoistone.com
	mail addr = support.neoistone.com
	serial = 2021111200
	refresh = 3600
	retry = 1800
	expire = 1209600
	minimum = 86400

Authoritative answers can be found from:
Query Port Number

Change the port number using which you want to connect

[manikantasripadi@linuxtips ~]$ nslookup -port 53 linuxtips.in

Server:		linuxtips.in
Address:	202.65.142.76#53

4. Command: dig

dig is a tool for querying DNS nameservers for information about host addresses, mail exchanges, nameservers, and related information. This tool can be used from any Linux (Unix) or Macintosh OS X operating system. The most typical use of dig is to simply query a single host.

[manikantasripadi@linuxtips ~]$ dig linuxtips.in

; <<>> DiG 9.10.6 <<>> linuxtips.in
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3301
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;linuxtips.in.			IN	A

;; ANSWER SECTION:
linuxtips.in.		12824	IN	A	202.65.142.76

;; Query time: 61 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Sun Dec 05 00:15:53 IST 2021
;; MSG SIZE  rcvd: 46

Turn Off Comment Lines

[manikantasripadi@linuxtips ~]$ dig linuxtips.in +nocomments 

; <<>> DiG 9.10.6 <<>> linuxtips.in +nocomments
;; global options: +cmd
;linuxtips.in.			IN	A
;; Query time: 4018 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Sun Dec 05 00:17:44 IST 2021
;; MSG SIZE  rcvd: 30

Turn Off Authority Section

[manikantasripadi@linuxtips ~]$ dig linuxtips.in +noauthority

; <<>> DiG 9.10.6 <<>> linuxtips.in +noauthority
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51135
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;linuxtips.in.			IN	A

;; ANSWER SECTION:
linuxtips.in.		10077	IN	A	202.65.142.76

;; Query time: 61 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Sun Dec 05 00:19:23 IST 2021
;; MSG SIZE  rcvd: 46

Turn Off Additional Section

[manikantasripadi@linuxtips ~]$ dig  linuxtips.in +noadditional

; <<>> DiG 9.10.6 <<>> linuxtips.in +noadditional
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 46815
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;linuxtips.in.			IN	A

;; ANSWER SECTION:
linuxtips.in.		10956	IN	A	202.65.142.76

;; Query time: 61 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Sun Dec 05 01:33:55 IST 2021
;; MSG SIZE  rcvd: 46

Turn Off Stats Section

[manikantasripadi@linuxtips ~]$ dig linuxtips.in +nostats 

; <<>> DiG 9.10.6 <<>> linuxtips.in +nostats
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51878
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;linuxtips.in.			IN	A

;; ANSWER SECTION:
linuxtips.in.		12066	IN	A	202.65.142.76

Turn Off Answer Section

[manikantasripadi@linuxtips ~]$ dig linuxtips.in +noanswer

; <<>> DiG 9.10.6 <<>> linuxtips.in +noanswer
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34684
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;linuxtips.in.			IN	A

;; Query time: 66 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Sun Dec 05 01:36:27 IST 2021
;; MSG SIZE  rcvd: 46

Disable All Section at Once

[manikantasripadi@linuxtips ~]$ dig linuxtips.in +noall

; <<>> DiG 9.10.6 <<>> linuxtips.in +noall
;; global options: +cmd 

5. Command: uptime

You have just connected to your Linux Server Machine and founds Something unusual or malicious, what you will do? Guessing…. NO, definitely not you could run uptime to verify what happened actually when the server was unattended.

[manikantasripadi@linuxtips ~]$ uptime
 1:39  up 7 days,  9:19, 3 users, load averages: 3.06 2.50 1.86

6. Command: wall

one of the most important command for administrator, wall sends a message to everybody logged in with their mesg permission set to “yes“. The message can be given as an argument to wall, or it can be sent to wall’s standard input.

[manikantasripadi@linuxtips ~]$ wall "we will be going down for maintenance for one hour sharply at 03:30 pm"

Broadcast message from root@linuxtips (pts/0) (Sat Jun 29 14:44:02 2013): 

we will be going down for maintenance for one hour sharply at 03:30 pm

7. command: mesg

Lets you control if people can use the “write” command, to send text to you over the screen.

mesg [n|y]
n - prevents the message from others popping up on the screen.
y – Allows messages to appear on your screen.

8. Command: write

Let you send text directly to the screen of another Linux machine if ‘mesg’ is ‘y’.

[manikantasripadi@linuxtips ~]$ write ravisaive

9. Command: talk

An enhancement to write command, talk command lets you talk to the logged in users.

[manikantasripadi@linuxtips ~]$ talk ravisaive

Note: If talk command is not installed, you can always apt or yum the required packages.

[manikantasripadi@linuxtips ~]$ yum install talk
OR
[manikantasripadi@linuxtips ~]$ apt-get install talk

10. Command: w

what command ‘w’ seems you funny? But actually it is not. t’s a command, even if it’s just one letter long! The command “w” is a combination of uptime and who commands given one immediately after the other, in that order.

[manikantasripadi@linuxtips ~]$ w

15:05:42 up  4:49,  3 users,  load average: 0.02, 0.01, 0.00 
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT 
server   tty7     :0               14:06    4:43m  1:42   0.08s pam: gdm-passwo 
server   pts/0    :0.0             14:18    0.00s  0.23s  1.65s gnome-terminal 
server   pts/1    :0.0             14:47    4:43   0.01s  0.01s bash

11. Command: rename

As the name suggests, this command rename files. rename will rename the specified files by replacing the first occurrence from the file name.

Give the file names a1, a2, a3, a4.....1213

Just type the command.

 rename a1 a0 a?
 rename a1 a0 a??

12. Command: top

Displays the processes of CPU. This command refresh automatically, by default and continues to show CPU processes unless interrupt-instruction is given.

[manikantasripadi@linuxtips ~]$ top

top - 14:06:45 up 10 days, 20:57,  2 users,  load average: 0.10, 0.16, 0.21
Tasks: 240 total,   1 running, 235 sleeping,   0 stopped,   4 zombie
%Cpu(s):  2.0 us,  0.5 sy,  0.0 ni, 97.5 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:   2028240 total,  1777848 used,   250392 free,    81804 buffers
KiB Swap:  3905532 total,   156748 used,  3748784 free,   381456 cached

  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+ COMMAND                                                                                                            
23768 ravisaiv  20   0 1428m 571m  41m S   2.3 28.9  14:27.52 firefox                                                                                                            
24182 ravisaiv  20   0  511m 132m  25m S   1.7  6.7   2:45.94 plugin-containe                                                                                                    
26929 ravisaiv  20   0  5344 1432  972 R   0.7  0.1   0:00.07 top                                                                                                                
24875 ravisaiv  20   0  263m  14m  10m S   0.3  0.7   0:02.76 lxterminal                                                                                                         
    1 root      20   0  3896 1928 1228 S   0.0  0.1   0:01.62 init                                                                                                               
    2 root      20   0     0    0    0 S   0.0  0.0   0:00.06 kthreadd                                                                                                           
    3 root      20   0     0    0    0 S   0.0  0.0   0:17.28 ksoftirqd/0                                                                                                        
    5 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 kworker/0:0H                                                                                                       
    7 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 kworker/u:0H                                                                                                       
    8 root      rt   0     0    0    0 S   0.0  0.0   0:00.12 migration/0                                                                                                        
    9 root      20   0     0    0    0 S   0.0  0.0   0:00.00 rcu_bh                                                                                                             
   10 root      20   0     0    0    0 S   0.0  0.0   0:26.94 rcu_sched                                                                                                          
   11 root      rt   0     0    0    0 S   0.0  0.0   0:01.95 watchdog/0                                                                                                         
   12 root      rt   0     0    0    0 S   0.0  0.0   0:02.00 watchdog/1                                                                                                         
   13 root      20   0     0    0    0 S   0.0  0.0   0:17.80 ksoftirqd/1                                                                                                        
   14 root      rt   0     0    0    0 S   0.0  0.0   0:00.12 migration/1                                                                                                        
   16 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 kworker/1:0H                                                                                                       
   17 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 cpuset                                                                                                             
   18 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 khelper                                                                                                            
   19 root      20   0     0    0    0 S   0.0  0.0   0:00.00 kdevtmpfs                                                                                                          
   20 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 netns                                                                                                              
   21 root      20   0     0    0    0 S   0.0  0.0   0:00.04 bdi-default                                                                                                        
   22 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 kintegrityd                                                                                                        
   23 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 kblockd                                                                                                            
   24 root       0 -20     0    0    0 S   0.0  0.0   0:00.00 ata_sff

13. Command: mkfs.ext4

This command create a new ext4 file system on the specified device, if wrong device is followed after this command, the whole block will be wiped and formatted, hence it is suggested not to run this command unless and until you understand what you are doing.

Mkfs.ext4 /dev/sda1 (sda1 block will be formatted)
mkfs.ext4 /dev/sdb1 (sdb1 block will be formatted)

14. Command: vi/emacs/nano

vi (visual), emacsnano are some of the most commonly used editors in Linux. They are used oftenly to edit text, configuration,… files. A quick guide to work around vi and nano is, emacs is a.

vi-editor

[manikantasripadi@linuxtips ~]$ touch a.txt (creates a text file a.txt) 
[manikantasripadi@linuxtips ~]$ vi a.txt (open a.txt with vi editor)

[press ‘i’ to enter insert mode, or you won’t be able to type-in anything]

echo "Hello"  (your text here for the file)
  1. alt+x (exit insert mode, remember to keep some space between the last letter.
  2. ctrl+x command or your last word will be deleted).
  3. :wq! (saves the file, with the current text, remember ‘!’ is to override).

nano editor

[manikantasripadi@linuxtips ~]$ nano a.txt (open a.txt file to be edited with nano)
edit, with the content, required

ctrl +x (to close the editor). It will show output as:

Save modified buffer (ANSWERING "No" WILL DESTROY CHANGES) ?                    
 Y Yes 
 N No           ^C Cancel

Click ‘y’ to yes and enter file name, and you are done.

15. Command: rsync

Rsync copies files and has a -P switch for a progress bar. So if you have rsync installed, you could use a simple alias.

alias cp='rsync -aP'

Now try to copy a large file in terminal and see the output with remaining items, similar to a progress bar.

Moreover, Keeping and Maintaining backup is one of the most important and boring work a system administrator, needs to perform. Rsync is a very nice tool (there exists, several other) to create and maintain backup, in terminal.

[manikantasripadi@linuxtips ~]$ rsync -zvr IMG_5267\ copy\=33\ copy\=ok.jpg ~/Desktop/ 

sending incremental file list 
IMG_5267 copy=33 copy=ok.jpg 

sent 2883830 bytes  received 31 bytes  5767722.00 bytes/sec 
total size is 2882771  speedup is 1.00

Note-z for compression, -v for verbose and -r for recursive.

16. Command: free

Keeping track of memory and resources is as much important, as any other task performed by an administrator, and ‘free‘ command comes to rescue here.

Current Usage Status of Memory

[manikantasripadi@linuxtips ~]$ free

             total       used       free     shared    buffers     cached
Mem:       2028240    1788272     239968          0      69468     363716
-/+ buffers/cache:    1355088     673152
Swap:      3905532     157076    3748456

Tuned Output in KB, or MB, or GB

[manikantasripadi@linuxtips ~]$ free -b

             total       used       free     shared    buffers     cached
Mem:    2076917760 1838272512  238645248          0   71348224  372670464
-/+ buffers/cache: 1394253824  682663936
Swap:   3999264768  160845824 3838418944
[manikantasripadi@linuxtips ~]$ free -k

             total       used       free     shared    buffers     cached
Mem:       2028240    1801484     226756          0      69948     363704
-/+ buffers/cache:    1367832     660408
Swap:      3905532     157076    3748456
[manikantasripadi@linuxtips ~]$ free -m

             total       used       free     shared    buffers     cached
Mem:          1980       1762        218          0         68        355
-/+ buffers/cache:       1338        641
Swap:         3813        153       3660
[manikantasripadi@linuxtips ~]$ free -g

             total       used       free     shared    buffers     cached
Mem:             1          1          0          0          0          0
-/+ buffers/cache:          1          0
Swap:            3          0          3

Check Current Usage in Human Readable Format

[manikantasripadi@linuxtips ~]$ free -h

             total       used       free     shared    buffers     cached
Mem:          1.9G       1.7G       208M         0B        68M       355M
-/+ buffers/cache:       1.3G       632M
Swap:         3.7G       153M       3.6G

Check Status Contineously After Regular Interval

[manikantasripadi@linuxtips ~]$ free -s 3

             total       used       free     shared    buffers     cached
Mem:       2028240    1824096     204144          0      70708     364180
-/+ buffers/cache:    1389208     639032
Swap:      3905532     157076    3748456

             total       used       free     shared    buffers     cached
Mem:       2028240    1824192     204048          0      70716     364212
-/+ buffers/cache:    1389264     638976
Swap:      3905532     157076    3748456

17. Command: mysqldump

Ok till now you would have understood what this command actually stands for, from the name of this command.mysqldump commands dumps (backups) all or a particular database data into a given a file.For example,

[manikantasripadi@linuxtips ~]$ mysqldump -u root -p --all-databases > /home/server/Desktop/backupfile.sql

Notemysqldump requires mysql to be running and correct password for authorisation. We have covered some useful “mysqldump” commands at Database Backup with mysqldump Command

18. Command: mkpasswd

Make a hard-to-guess, random password of the length as specified.

[root@compute-2 ~]# yum install expect
Failed to set locale, defaulting to C
Loaded plugins: fastestmirror, universal-hooks
Loading mirror speeds from cached hostfile
 * EA4: 103.48.119.120
 * cpanel-addons-production-feed: 103.48.119.120
 * cpanel-plugins: 103.48.119.120
 * base: download.cf.centos.org
 * epel: mirrors.nipa.cloud
 * extras: download.cf.centos.org
 * updates: download.cf.centos.org
Resolving Dependencies
--> Running transaction check
---> Package expect.x86_64 0:5.45-14.el7_1 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
 Package          Arch             Version                 Repository      Size
================================================================================
Installing:
 expect           x86_64           5.45-14.el7_1           base           262 k

Transaction Summary
================================================================================
Install  1 Package

Total download size: 262 k
Installed size: 566 k
Is this ok [y/d/N]: y
Downloading packages:
expect-5.45-14.el7_1.x86_64.rpm                            | 262 kB   00:00     
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : expect-5.45-14.el7_1.x86_64                                  1/1 
  Verifying  : expect-5.45-14.el7_1.x86_64                                  1/1 

Installed:
  expect.x86_64 0:5.45-14.el7_1                                                 

Complete!
[root@compute-2 ~]# mkpasswd -l 10

s37tGme|jW
[root@compute-2 ~]# mkpasswd -l 20 

l6Rbzihpnb5nbkzyu^uB

Note-l 10 generates a random password of 10 characters while -l 20 generates a password of character 20, it could be set to anything to get desired result. This command is very useful and implemented in scripting language oftenly to generate random passwords. You might need to yum or apt the ‘expect’ package to use this command.

59. Command: paste

Merge two or more text files on lines using. Example. If the content of file1 was:

1 
2 
3 

and file2 was: 

a 
b 
c 
d 
the resulting file3 would be: 

1    a 
2    b 
3    c 
     d

60.Command: lsof

lsof stands for “list open files” and displays all the files that your system has currently opened. It’s very useful to figure out which processes uses a certain file, or to display all the files for a single process.

[manikantasripadi@linuxtips ~]$ lsof 

COMMAND     PID   TID            USER   FD      TYPE     DEVICE SIZE/OFF       NODE NAME
init          1                  root  cwd       DIR        8,1     4096          2 /
init          1                  root  rtd       DIR        8,1     4096          2 /
init          1                  root  txt       REG        8,1   227432     395571 /sbin/init
init          1                  root  mem       REG        8,1    47080     263023 /lib/i386-linux-gnu/libnss_files-2.17.so
init          1                  root  mem       REG        8,1    42672     270178 /lib/i386-linux-gnu/libnss_nis-2.17.so
init          1                  root  mem       REG        8,1    87940     270187 /lib/i386-linux-gnu/libnsl-2.17.so
init          1                  root  mem       REG        8,1    30560     263021 /lib/i386-linux-gnu/libnss_compat-2.17.so
init          1                  root  mem       REG        8,1   124637     270176 /lib/i386-linux-gnu/libpthread-2.17.so
init          1                  root  mem       REG        8,1  1770984     266166 /lib/i386-linux-gnu/libc-2.17.so
init          1                  root  mem       REG        8,1    30696     262824 /lib/i386-linux-gnu/librt-2.17.so
init          1                  root  mem       REG        8,1    34392     262867 /lib/i386-linux-gnu/libjson.so.0.1.0
init          1                  root  mem       REG        8,1   296792     262889 /lib/i386-linux-gnu/libdbus-1.so.3.7.2
init          1                  root  mem       REG        8,1    34168     262840 /lib/i386-linux-gnu/libnih-dbus.so.1.0.0
init          1                  root  mem       REG        8,1    95616     262848 /lib/i386-linux-gnu/libnih.so.1.0.0
init          1                  root  mem       REG        8,1   134376     270186 /lib/i386-linux-gnu/ld-2.17.so
init          1                  root    0u      CHR        1,3      0t0       1035 /dev/null
init          1                  root    1u      CHR        1,3      0t0       1035 /dev/null
init          1                  root    2u      CHR        1,3      0t0       1035 /dev/null
init          1                  root    3r     FIFO        0,8      0t0       1714 pipe
init          1                  root    4w     FIFO        0,8      0t0       1714 pipe
init          1                  root    5r     0000        0,9        0       6245 anon_inode
init          1                  root    6r     0000        0,9        0       6245 anon_inode
init          1                  root    7u     unix 0xf5e91f80      0t0       8192 @/com/ubuntu/upstart