Linux Commands

Info (List all the available command info )

$ info

which command gives the command location / source path

$ which ls

output: /usr/bin/ls

Hard link

Link Guide \

$ link fileExist.txt newLinkFile.txt

• The file name and the file's data are two separate entities.

List all files including inode

$ ls -li

How to find all hard links to a given file / Find out all hard links of inode 531188

$ find / -inum 531188

Gives a list of all files which have more than one link.

$ find . -type f -links +1 2>/dev/null

How can I make ls only display files?

Method-1

$ls -p | grep -v / \

$ls -p | grep -v / | column

Using ls -p tells ls to append a slash to entries which are a directory, and using grep -v / tells grep to return only lines not containing a slash.

• p adds the forward slash ('/') to the directory names
• r reverses the order of output
• v lets grep do an inverse search to print everything except the directories (everything that doesn't have the '/' that -p put there)
• column puts it in columns

Method-2

find . -maxdepth 1 -not -type d

Method-3

ls -p | egrep -v /$

Method-4

ls -F | grep -v /

Above command displays files, But it includes symlinks, pipes, etc. If you want to eliminate them too, you can use one of the flags mentioned below.

ls -F appends symbols to filenames. These symbols show useful information about files.

• @ means symbolic link (or that the file has extended attributes).
• * means executable.
• = means socket.
• | means named pipe.
• > means door.
• / means directory.

ls -F | grep -Ev '/|@|*|=|\|'

ls -F | grep -Ev '/|@|*|=|>|\|'

How to get package info (using package manager dpkg)

$ whatis dpkg

$ which column

$ dpkg -S $(which column)

Check the ip address

$ ip address

Deafult permission | umask command

Default File Permission

• Files: rw-rw-rw- (666)
• Directories: rwxrwxrwx (777)

Get the umask value

$ umask

Lets assume your umask value is 002
octal to binary to mode
002 --> 010 --> -w-

Now create a file called: student.txt
Calculate the mode value beforehand:
rw- rw- rw-
--- --- -w-
----------------
rw- rw- r-- ==> 664

Now check the student.txt file permssion using ls -l or stat command $ stat student.txt

Concatenate Command -cat

It reads data from the file and gives their content as output. It helps us to create, view, concatenate files

`cat > file1.txt master-academy to save and close use ctrl+d

` > `cat -n file1.txt` > show content with line numbers

cat file1.txt > file2.txt overright one file by another

tac file1.txt content display in reverse order

cat file1.txt file2.txt view content from multiple files

cat file1.txt file2.txt > file3.txt combines multiple files output into a new file

cat file1.txt >> file2.txt to append the file1.txt to file2.txt

cat file1.txt | cat >> other.txt pipeing one file output appending into other file

Changing the Time Zone in Linux

timedatectl

List current time zone

ls -l /etc/localtime

List all existing time zone

timedatectl list-timezones
example time zone: Asia/Dhaka

sudo timedatectl set-timezone <your_time_zone>

sudo timedatectl set-timezone Asia/Dhaka

References:

• Hard link
• LS Display
• Unmask