Linux is one of the most popular operating systems for developers and hackers. Today we are going to highlight some of the advanced Linux commands which are being used by regular Linux user in order to make his system keep running smoothly and well configured. Linux is such an OS which could be configured in any required way, as per the user’s knowledge and requirement.
You get full control over every module of the system which could be configured and restricted in the way you need.
Here are some useful commands.
Also, Read: 10 Reasons why Linux is better for programmers
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.
- ifconfig, when invoked with no arguments will display all the details of currently active interfaces. If you give the interface name as an argument, the details of that specific interface will be displayed.
# ifconfig eth0 eth0 Link encap:Ethernet HWaddr 00:2D:32:3E:39:3B inet addr:192.168.2.2 Bcast:192.168.2.255 Mask:255.255.255.0 inet6 addr: fe80::21d:92ff:fede:499b/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:977839669 errors:0 dropped:1990 overruns:0 frame:0 TX packets:1116825094 errors:8 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:2694625909 (2.5 GiB) TX bytes:4106931617 (3.8 GiB) Interrupt:185 Base address:0xdc00
- Display Details of All interfaces Including Disabled Interfaces
# ifconfig -a
- Disable an Interface
# ifconfig eth0 down
- Enable an Interface
# ifconfig eth0 up
- Assign ip-address to an Interface
# ifconfig eth0 192.168.2.2
- Change MTU
# ifconfig eth0 mtu XX
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
[root@root ~]$ 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
[root@root ~]$ 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
[root@root ~]$ 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 ....
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.
- Query Mail Exchanger Record
[root@root ~]$ nslookup -query=mx abc.com Server: 192.168.1.1 Address: 192.168.1.1#53 Non-authoritative answer: abc.com mail exchanger = 0 smtp.secureserver.net. abc.com mail exchanger = 10 mailstore1.secureserver.net. Authoritative answers can be found from:
- Query Name Server
[root@root ~]$ nslookup -type=ns abc.com Server: 192.168.1.1 Address: 192.168.1.1#53 Non-authoritative answer: abc.com nameserver = ns3404.com. abc.com nameserver = ns3403.com. Authoritative answers can be found from:
- Query DNS Record
[root@root ~]$ nslookup -type=any abc.com Server: 192.168.1.1 Address: 192.168.1.1#53 Non-authoritative answer: abc.com mail exchanger = 10 mailstore1.secureserver.net. abc.com mail exchanger = 0 smtp.secureserver.net. abc.com nameserver = ns06.domaincontrol.com. abc.com nameserver = ns3404.com. abc.com nameserver = ns3403.com. abc.com nameserver = ns05.domaincontrol.com. Authoritative answers can be found from:
- Query Start of Authority
[root@root ~]$ nslookup -type=soa abc.com Server: 192.168.1.1 Address: 192.168.1.1#53 Non-authoritative answer: abc.com origin = ns3403.hostgator.com mail addr = dnsadmin.gator1702.hostgator.com serial = 2012081102 refresh = 86400 retry = 7200 expire = 3600000 minimum = 86400 Authoritative answers can be found from:
4 : Command: dig
a 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
- Turn Off Comment Lines
[root@root ~]$ dig abc.com +nocomments ; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6 <<>> tecmint.com +nocomments ;; global options: +cmd ;abc.com. IN A abc.com. 14400 IN A 40.216.66.239 ;; Query time: 418 msec ;; SERVER: 192.168.1.1#53(192.168.1.1) ;; WHEN: Sat Jun 29 13:53:22 2013 ;; MSG SIZE rcvd: 45
- Turn Off Authority Section
[root@root ~]$ dig abc.com +noauthority ; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6 <<>> tecmint.com +noauthority ;; global options: +cmd ;; Got answer: ;; ->>HEADER<
- Disable All Section at Once
[root@root ~]$ dig tecmint.com +noall ; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.17.rc1.el6 <<>> tecmint.com +noall ;; global options: +cmd
5 : Command: top
Displays the processes of CPU. This command refreshes automatically, by default and continues to show CPU processes unless interrupt-instruction is given.
[root@root ~]$ 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
6 : Command: mkfs.ext4
This command creates a new ext4 file system on the specified device, if the 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)
7 : Command: vi/emacs/nano
vi (visual), emacs, nano are some of the most commonly used editors in Linux. They are used often to edit text, configuration,… files. A quick guide to work around vi and nano is, emacs is a.
- vi-editor
[root@root ~]$ touch a.txt (creates a text file a.txt)
[root@root ~]$ 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)
* alt+x (exit insert mode, remember to keep some space between the last letter.
* ctrl+x command or your last word will be deleted).
* :wq! (saves the file, with the current text, remember ‘!’ is to override).
- nano editor
[root@root ~]$ 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 the file name, and you are done.
8 : 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 works a system administrator, needs to perform. Rsync is a very nice tool (there exists, several other) to create and maintain the backup, in the terminal.
[root@root ~]$ 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
9 : Command: mysqldump
From the name, it is understood what this command actually stands for, from the name of this command.mysqldump commands dump (backups) all or a particular database data into a given a file. For example,
[root@root ~]$ mysqldump -u root -p --all-databases > /home/server/Desktop/backupfile.sql
Note: mysqldump requires MySQL to be running and correct password for authorization
10 : 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.
[root@root ~]$ uptime 14:37:10 up 4:21, 2 users, load average: 0.00, 0.00, 0.04
11 : Command: talk
An enhancement to write command, talk command lets you talk to the logged in users.
[root@root ~]$ talk ravisaive
Note: If talk command is not installed, you can always apt or yum the required packages.
[root@root ~]$ yum install talk
OR
[root@root ~]$ apt-get install talk
12 : Command: w
what command ‘w’ seems you funny? But actually, it is not. it’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.
[root@root ~]$ 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
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