Practical uses of Linux Command

1. cp

a. It is a command which is used to copy the files or directories from one place to another place.

Example:

~$ cp Topics.odt /home/anil/Downloads/

~$

Real Time Problem: Suppose you are working in a company and your manager ask you to copy the file in one more location. At this point of time above example help you.

b. We can preserve the permission of the files or directories while copying from source to destination.

Example:

~$ cp -dR --preserve=all Text.txt /home/anil/Downloads

Real Time Problem: Suppose you are working in a company and your manager ask you to copy the file in to another location by preserving the ownership and permission of the file. At this point of time above example help you.

2. scp

a. It is a command which is used to copy files over the network between the host.

Example:

~# scp /home/anil/Text.txt anil@127.0.0.1:/home/anil

anil@127.0.0.1's password:

Text.txt 100% 38 0.0KB/s 00:00

Real Time Problem: Suppose you are working in a company and your manager ask you to copy the file in to another remote machine . At this point of time above example help you.

b. We can use v option to debug messages about their progress , authentication and configuration

problems.

Example:

~# scp -v /home/anil/Text.txt anil@127.0.0.1:/home/anil

Executing: program /usr/bin/ssh host 127.0.0.1, user anil, command scp -v -t /home/anil

OpenSSH_6.6.1, OpenSSL 1.0.1f 6 Jan 2014

debug1: Reading configuration data /etc/ssh/ssh_config

debug1: /etc/ssh/ssh_config line 19: Applying options for *

debug1: Connecting to 127.0.0.1 [127.0.0.1] port 22.

debug1: Connection established.

debug1: permanently_set_uid: 0/0

debug1: identity file /root/.ssh/id_rsa type -1

debug1: identity file /root/.ssh/id_rsa-cert type -1

debug1: identity file /root/.ssh/id_dsa type -1

debug1: identity file /root/.ssh/id_dsa-cert type -1

debug1: identity file /root/.ssh/id_ecdsa type -1

debug1: identity file /root/.ssh/id_ecdsa-cert type -1

debug1: identity file /root/.ssh/id_ed25519 type -1

debug1: identity file /root/.ssh/id_ed25519-cert type -1

debug1: Enabling compatibility mode for protocol 2.0

debug1: Local version string SSH-2.0-OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.8

debug1: Remote protocol version 2.0, remote software version OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.8

debug1: match: OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.8 pat OpenSSH_6.6.1* compat 0x04000000

debug1: SSH2_MSG_KEXINIT sent

debug1: SSH2_MSG_KEXINIT received

debug1: kex: server->client aes128-ctr hmac-md5-etm@openssh.com none

debug1: kex: client->server aes128-ctr hmac-md5-etm@openssh.com none

debug1: sending SSH2_MSG_KEX_ECDH_INIT

debug1: expecting SSH2_MSG_KEX_ECDH_REPLY

debug1: Server host key: ECDSA a2:a9:cf:6f:4a:39:51:bd:64:31:a6:70:6b:dc:4d:01

debug1: Host '127.0.0.1' is known and matches the ECDSA host key.

debug1: Found key in /root/.ssh/known_hosts:13

debug1: ssh_ecdsa_verify: signature correct

debug1: SSH2_MSG_NEWKEYS sent

debug1: expecting SSH2_MSG_NEWKEYS

debug1: SSH2_MSG_NEWKEYS received

debug1: SSH2_MSG_SERVICE_REQUEST sent

debug1: SSH2_MSG_SERVICE_ACCEPT received

debug1: Authentications that can continue: publickey,password

debug1: Next authentication method: publickey

debug1: Trying private key: /root/.ssh/id_rsa

debug1: Trying private key: /root/.ssh/id_dsa

debug1: Trying private key: /root/.ssh/id_ecdsa

debug1: Trying private key: /root/.ssh/id_ed25519

Real Time Problem: Suppose you are working in a company and your manager ask you to copy the file in to another remote machine but while copying you are getting some error . At this point of time above example help you.

3. rsync

a. It is a fast and extraordinarily versatile file copying tool.

Example:

~# rsync /home/anil/Text.txt anil@127.0.0.1:/home/anil

anil@127.0.0.1's password:

b. -avz option is used to sync the file by preserving the ownership and permission.

Real Time Problem: Suppose you are working in a company and your manager ask you to sync the source and destination folder. At this point of time above example help you.

Example:

~# rsync -avz /home/anil/T* /home/anil/Downloads/

sending incremental file list

sent 205,086 bytes received 287 bytes 136,915.33 bytes/sec

total size is 242,625 speedup is 1.18

Real Time Problem: Suppose you are working in a company and your manager ask you to preserve the ownership and permission of the files while copying the files. At this point of time above example help you.

4. mv

a. It is a linux command which is used to rename the files.

Example:

~$ mv Text.txt New.txt

Real Time Problem: Suppose you are working in a company and your manager ask you to rename the file. At this point of time above example help you.

5. SSH

a. It is a program for logging into a remote machine and for executing commands on a remote

machine.

Example:

~$ ssh anil@localhost

anil@localhost's password:

Welcome to Ubuntu 14.04.4 LTS (GNU/Linux 4.2.0-27-generic x86_64)

* Documentation: https://help.ubuntu.com/

655 packages can be updated.

0 updates are security updates.

New release '16.04.5 LTS' available.

Run 'do-release-upgrade' to upgrade to it.

Real Time Problem: Suppose you are working in a company and your manager ask you to login to the specific remote machine. At this point of time above example help you.

b. With the help of ssh we can execute the commands on a remote machine.

Example:

~# ssh anil@localhost ls

Real Time Problem: Suppose you are working in a company and your manager ask you to login to the remote system and run the ls command. At this point of time above example help you.

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6. dmesg

a. It is a linux command which is used to read all messages from kernel ring buffer.

Example:

~$ dmesg

Real Time Problem: Suppose you are working in a company and your manager ask you to login to the remote system and check the kernel messages. At this point of time above example help you.

b. We can read all the kernel messages with timestamp by using option -T along with dmesg command.

Example:

~$ dmesg -T

[Tue Oct 30 11:24:05 2018] traps: chrome[5119] trap invalid opcode ip:55ea9a282f7b sp:7ffc8ad4aa30 error:0 in chrome[55ea96009000+5df9000]

[Tue Oct 30 11:24:29 2018] traps: chrome[5255] trap invalid opcode ip:55ea9a282f7b sp:7ffc8ad4aad0 error:0 in chrome[55ea96009000+5df9000]

Real Time Problem: Suppose you are working in a company and your manager ask you to login to the remote system and check the kernel messages with timestamp. At this point of time above example help you.

7. lsof

a. It lists all the open files related belonging to all active processes.

Example:

~$ lsof

BrowserBl 2488 2803 anil mem REG 8,1 34624 12591322 /usr/lib/x86_64-linux-gnu/libogg.so.0.8.1

BrowserBl 2488 2803 anil mem REG 8,1 182584 12591594 /usr/lib/x86_64-linux-gnu/libvorbis.so.0.4.5

Real Time Problem: Suppose you are working in a company and your manager ask you to login to the remote system and check all the open file related to the active processes. At this point of time above example help you.

b. We can use -N option to list all the NFS files.

Example:

~$ lsof -N

Real Time Problem: Suppose you are working in a company and your manager ask you to login to the remote system and check all the NFS files related to the active processes. At this point of time above example help you.

8. Chattr

a. It is a linux file utility which is used to secure linux files or directories from accidential deletion.

Example:

~# chattr +i New.txt

root@anil-Vostro-3446:~# rm -rf New.txt

rm: cannot remove ‘New.txt’: Operation not permitted

Real Time Problem: Suppose you are working in a company and your manager ask you secure the New.txt file. At this point of time above example help you.

b. With the help of -R option we can secure entire directory.

Example:

~# chattr -R +i Training/

root@anil-Vostro-3446:~# rm -rf Training/

rm: cannot remove ‘Training/data1.zip’: Permission denied

rm: cannot remove ‘Training/data.zip’: Permission denied

rm: cannot remove ‘Training/sd.txt’: Permission denied

rm: cannot remove ‘Training/Untitled Document~’: Permission denied

rm: cannot remove ‘Training/Untitled Document’: Permission denied

rm: cannot remove ‘Training/dat.tar’: Permission denied

rm: cannot remove ‘Training/text.txt’: Permission denied

Real Time Problem: Suppose you are working in a company and your manager ask you secure the entire directory. At this point of time above example help you.

9. Finger

a. It is a user information lookup program.

Example:

~$ finger anil

Login: anil Name: This is local user

Directory: /home/anil Shell: /bin/bash

On since Thu Nov 1 09:45 (IST) on :0 from :0 (messages off)

On since Thu Nov 1 11:14 (IST) on pts/1 from :0

1 day 21 hours idle

On since Thu Nov 1 11:16 (IST) on pts/11 from :0

1 day 20 hours idle

On since Fri Nov 2 17:00 (IST) on pts/14 from :0

2 seconds idle

On since Fri Nov 2 17:03 (IST) on pts/27 from :0

15 hours 12 minutes idle

No mail.

No Plan.

Real Time Problem: Suppose you are working in a company and your manager ask you to send the user information. At this point of time above example help you.

10. fsck

a. It is used to check and repair the filesystem.

Example:

~# fsck /dev/sdb

fsck from util-linux 2.20.1

fsck.fat 3.0.26 (2014-03-07)

0x41: Dirty bit is set. Fs was not properly unmounted and some data may be corrupt.

1) Remove dirty bit

2) No action

? 1

Leaving filesystem unchanged.

/dev/sdb: 2 files, 61/1992903 clusters

Real Time Problem: Suppose you are working in a company and your manager ask you to verify the /dev/sdb. At this point of time above example help you.

b. We can use -y option to automatically fix all the problems.

Example:

~# fsck -y /dev/sdb

fsck from util-linux 2.20.1

fsck.fat 3.0.26 (2014-03-07)

0x41: Dirty bit is set. Fs was not properly unmounted and some data may be corrupt.

Automatically removing dirty bit.

Performing changes.

/dev/sdb: 2 files, 61/1992903 clusters

Real Time Problem: Suppose you are working in a company and your manager ask you to verify and correct all the issue of the /dev/sdb automatically. At this point of time above example help you.

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