![Linux](https://cdn-0.reconshell.com/wp-content/uploads/2022/06/Pinguino.jpg)
Linux is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged in a Linux distribution.
Linux is used in the following ways: Server OS for web servers, database servers, file servers, email servers and any other type of shared server. Designed to support high-volume and multithreading applications, Linux is well-suited for all types of server applications. Desktop OS for personal productivity computing.
# 1. User Information
- who It is used to get information about currently logged in user on to system. If you don’t provide any option or arguments, the command displays the following information for each logged-in user.
- Login name of the user
- User terminal
- Date & Time of login
- Remote host name of the user
$ who admin tty2 2022-02-10 01:36 (tty2) root pts/1 2022-02-15 00:29 (10.190.95.154)
- whoami: It display the system’s username
$ whoami Avani Punita
- id: It display the user identification ( the real and effective user and group IDs ) information
$ id uid=1000(sj) gid=1000(sj) groups=1000(sj),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),120(lpadmin),131(lxd),132(sambashare)
- groups: This command is used to display all the groups for which the user belongs to.
$ group sj: sj, adm, cdrom, sudo, dip, plugdev, lpadmin, lxd, sambashare
- users: Displays usernames of all users currently logged on the system.
$ users root
- grep: It is a powerful pattern searching tool to find information about a specific user from the system accounts file: /etc/passwd.
$ grep -i sj /etc/passwd sj:x:1000:1000:sj,,,:/home/sj:/bin/bash
- W Command: It(W) is a command-line utility that displays information about currently logged in users and what each user is doing.
w [OPTIONS] [USER] Example: w 18:45:04 up 2:09, 1 user, load average: 0.09, 0.07, 0.02 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT sj :0 :0 01:27 ?xdm? 1:14 0.01s /usr/lib/gdm3/g
- last or lastb: Displays a list of last logged in users on the system. You can pass user names to display their login and hostname details.
last [options] [username...] [tty...] Example: root pts/1 xx.xxx.xx.xxx Tue Feb 15 00:29 still logged in root pts/2 xx.xxx.xx.xxx Mon Feb 14 03:45 - 06:59 (03:13) root pts/1 xx.xxx.xx.xxx Mon Feb 14 01:21 - 04:35 (03:13) root pts/1 xx.xxx.xx.xxx Sun Feb 13 21:28 - 00:43 (03:15) root pts/1 xx.xxx.xx.xxx Sun Feb 13 09:46 - 10:20 (00:33) root pts/1 xx.xxx.xx.xxx Sat Feb 12 21:30 - 23:44 (02:13) root pts/1 xx.xxx.xx.xxx Sat Feb 12 11:15 - 11:56 (00:40) root pts/1 xx.xxx.xx.xxx Sat Feb 12 11:08 - 11:15 (00:06) root pts/1 xx.xxx.xx.xxx Sat Feb 12 02:06 - 05:19 (03:12)
- lastlog: The
lastlog
command is used to find the details of a recent login of all users or of a given user.
$ lastlog Username Port From Latest root pts/1 xx.xxx.xx.xxx Tue Feb 15 00:29:27 -0500 2022 daemon **Never logged in** bin **Never logged in** sys **Never logged in** sync **Never logged in** games **Never logged in** man **Never logged in** lp **Never logged in** mail **Never logged in** news **Never logged in**
# 2. Directory Commands
- pwd The pwd ( Present Working Directory ) command is used to print the name of the present/current working directory starting from the root.
$ pwd /home/sj/Desktop/Linux
- mkdir The mkdir ( make directory ) command allows users to create directories or folders.
$ mkdir ubuntu $ ls ubuntu
The option ‘-p’ is used to create multiple directories or parent directories at once.
$ mkdir -p dir1/dir2/dir3 $ cd dir1/dir2/dir3 ~/Desktop/Linux/dir1/dir2/dir3$
- rmdir: The rmdir ( remove directories ) is used to remove empty directories. Can be used to delete multiple empty directories as well. Safer to use compared to
rm -r FolderName
. This command can also be forced to delete non-empty directories.- Remove empty directory:
rmdir FolderName
- Remove multiple directories:
rmdir FolderName1 FolderName2 FolderName3
- Remove non-empty directories:
rmdir FolderName1 --ignore-fail-on-non-empty
- Remove entire directory tree. This command is similar to
rmdir a/b/c a/b a
:
rmdir -p a/b/c
- rm: The rm ( remove ) command is used to remove objects such as files, directories, symbolic links etc from the file system.
- Remove file: The rm command is used to remove or delete a file
rm file_name
- Remove file forcefully: The rm command with -f option is used for removal of file without prompting for confirmation.
rm -f filename
- Remove directory: The rm command with -r option is used to remove the directory and its contents recursively.
rm -r myDir
- Remove directory forcefully: The rm command with -rf option is used to forcefully remove directory recursively.
rm -rf myDir
- touch: The touch command is is used to create, change and modify timestamps of a file without any content.
- Create a new file: You can create a single file at a time using touch command. The file created is an empty file.touch file_name
- Create multiple files: You can create the multiple numbers of files at the same time.touch file1_name file2_name file3_name
- Change access time: The touch command with
a
option is used to change the access time of a file.touch -a file_name - Change modification time: The touch command with
m
option is used to change the modified time.touch -m file_name - Use timestamp of other file: The touch command with
r
option is used to get timestamp of another file.touch -r file2 file1In the above example, we get the timestamp of file1 for file2. - Create file with Specific time: The touch command with ‘t’ option is used to create a file with specified time.touch -t 1911010000 file_name
- cat: The cat command is used to create single or multiple files, view contain of file, concatenate files and redirect output in terminal or files.
- View file contents: You can view contents of a single or more files by mentioning the filenames.cat file_name1 file_name2
# 3. File Commands
Sl.No. | Commands | Description |
---|---|---|
01. | ls | directory listing |
02. | ls -al | formatted listing with hidden files |
03. | cd dir | change directory to dir |
04. | cd | change to home |
05. | pwd | show current directory |
06. | mkdir dir | create a directory dir |
07. | rm file | delete file |
08. | rm -r dir | delete directory dir |
09. | rm -f file | force remove file |
10. | rm -rf dir | force remove directory dir * |
11. | cp file1 file2 | copy file1 to file2 |
12. | cp -r dir1 dir2 | copy dir1 to dir2; create dir2 if it doesn’t exist |
13. | mv file1 file2 | rename or move file1 to file2 if file2 is an existing directory, moves file1 into directory file2 |
14. | ln -s file link | create symbolic link link to file |
15. | touch file | create or update file |
16. | cat > file | places standard input into file |
17. | more file | output the contents of file |
18. | head file | output the first 10 lines of file |
19. | tail file | output the last 10 lines of file |
20. | tail -f file | output the contents of file as it grows, starting with the last 10 lines |
# 4. File Permissions
- chmod octal file – change the permissions of file to octal, which can be found separately for user, group, and world by adding
- 4 – read (r)
- 2 – write (w)
- 1 – execute (x)
Examples
chmod 777
– read, write, execute for allchmod 755
– rwx for owner, rx for group and world
Since Linux is a multi-user operating system, it is necessary to provide security to prevent people from accessing each other’s confidential files. So Linux divides authorization into 2 levels,
- Ownership: Each file or directory has assigned with 3 types of owners i. User: Owner of the file who created it. ii. Group: Group of users with the same access permissions to the file or directory. iii. Other: Applies to all other users on the system
- Permissions: Each file or directory has following permissions for the above 3 types of owners.i. Read: Give you the authority to open and read a file and lists its content for a directory.ii. Write: Give you the authority to modify the contents of a file and add, remove and rename files stored in the directory.iii. Execute: Give you the authority to run the program in Unix/Linux.The permissions are indicated with below characters,
r = read permission w = write permission x = execute permission \- = no permission
The above authorization levels represented in a diagram
![perm](https://cdn-0.reconshell.com/wp-content/uploads/2022/06/permissions.png)
There is a need to restrict own file/directory access to others.
Change access: The chmod
command is used to change the access mode of a file. This command is used to set permissions ( read, write, execute ) on a file/directory for the owner, group and the others group.
chmod [reference][operator][mode] file... Example chmod ugo-rwx test.txt
There are 2 ways to use this command,
- Absolute mode: The file permissions will be represented in a three-digit octal number.The possible permissions types represented in a number format as below.
Permission Type | Number | Symbol |
---|---|---|
No Permission | 0 | — |
Execute | 1 | –x |
Write | 2 | -w- |
Execute + Write | 3 | -wx |
Read | 4 | r– |
Read + Execute | 5 | r-x |
Read + Write | 6 | rw- |
Read + Write + Execute | 7 | rwx |
Let’s update the permissions in absolute mode with an example as below,
chmode 764 test.txt
- Symbolic mode: In the symbolic mode, you can modify permissions of a specific owner unlike absolute mode.The owners are represented as below,OwnerDescriptionuuser/ownerggroupootheraalland the list of mathematical symbols to modify the file permissions as follows,OperatorDescription+Adds permission-Removes the permission=Assign the permission
Changing Ownership and Group: It is possible to change the the ownership and group of a file/directory using chown
command.
chown user filename chown user:group filename Example: chown John test.txt chown John:Admin test.txt
Change group-owner only: Sometimes you may need to change group owner only. In this case, chgrp command need to be used
chgrp group_name filename Example: sudo chgrp Administrator test.txt
# | Permission | rwx | Binary |
---|---|---|---|
7 | read, write and execute | rwx | 111 |
6 | read and write | rw- | 110 |
5 | read and execute | r-x | 101 |
4 | read only | r– | 100 |
3 | write and execute | -wx | 011 |
2 | write only | -w- | 010 |
1 | execute only | –x | 001 |
0 | none | — | 000 |
For a directory, execute means you can enter a directory.
User | Group | Others | Description |
---|---|---|---|
6 | 4 | 4 | User can read and write, everyone else can read ( Default file permissions ) |
7 | 5 | 5 | User can read, write and execute, everyone else can read and execute ( Default directory permissions ) |
- u – User
- g – Group
- o – Others
- a – All of the above
ls -l /foo.sh # List file permissions chmod +100 foo.sh # Add 1 to the user permission chmod -100 foo.sh # Subtract 1 from the user permission chmod u+x foo.sh # Give the user execute permission chmod g+x foo.sh # Give the group execute permission chmod u-x,g-x foo.sh # Take away the user and group execute permission chmod u+x,g+x,o+x foo.sh # Give everybody execute permission chmod a+x foo.sh # Give everybody execute permission chmod +x foo.sh # Give everybody execute permission
# 5. Networking
- Display network information:
ifconfig
command is used to display all network information ( ip address, ports etc )
ifconfig -a
- Test connection to a remote machine: Send an echo request to test connection of a remote machine.ping <ip-address> or hostname Example: ping 10.0.0.11
- Show IP Address: Display ip address of a currennt machinehostname -I (OR) ip addr show
- Active ports: Shows active or listening portsnetstat -pnltu
- Find information about domain:
whois
command is used to find out information about a domain, such as the owner of the domain, the owner’s contact information, and the nameservers used by domain.whois [domain] Example: whois google.com
# 6. Installing Packages
- Install package:
yum install package_name
- Package description: The info command is used to display brief details about a package.
yum info package_name
- Uninstall package: The remove command is used to remove or uninstall package name.
yum remove package_name
- Install package from local file:
It is also possible to install package from local file named package_name.rpm.
rpm -i package_name.rpm
- Install from source code:
tar zxvf sourcecode.tar.gz cd sourcecode ./configure make make install
# 7. Disk Usage
- Synopsis:
du
command is used to check the information of disk usage of files and directories on a machine
du [OPTION]... [FILE]...
- Disk usage of a directory: To find out the disk usage summary of a /home/ directory tree and each of its sub directories
du /home/
- Disk usage in human readable format: To find out the disk usage in human readable format
du -h /home/
- Total disk usage of a directory: To find out the total disk usage
du -sh /home/
- Total disk usage of all files and directories: To find out the total disk usage of files and directories
du -ah /home/
- Total disk usage of all files and directories upto certain depth: print the total for a directory only if it is N or fewer levels below the command
du -ah --max-depth 2 /home/
- Total disk usage with excluded files: To find out the total disk usage of files and directories, but excludes the files that matches given pattern.
du -ah --exclude="*.txt" /home/
- Help: This command gives information about
du
du --help
# 8. System and Hardware Information
- Print all information:
uname
is mainly used to print system information.
$ uname -a
- Print kernel name:
$ uname -s
- Print kernel release:
$ uname -r
- Print Architecture:
$ uname -m
- Print Operating System:
$ uname -o
# 9. Search Files
- Pattern search: The
grep
command is used to search patterns in files.
grep pattern files grep -i // Case sensitive grep -r // Recursive grep -v // Inverted search Example: grep "^hello" test.txt // Hello John grep -i "hELLo" text.txt // Hello John
- Find files and directories:
The find
command is used to find or search files and directories by file name, folder name, creation date, modification date, owner and permissions etc and perform subsequent operations on them.
i. Search file with name:
find ./directory_name -name file_name Example: find ./test -name test.txt // ./test/test.txt
ii. Search file with pattern:
find ./directory_name -name file_pattern Example: find ./test -name *.txt // ./test/test.txt
iii. Search file with executable action:
find ./directory_name -name file_name -exec command Example: find ./test -name test.txt -exec rm -i {} \; // Search file and delete it after confirmation
iv. Search for empty files or directories:
The find command is used to search all empty folders and files in the entered directory or sub-directories.
find ./directory_name -empty Example: find ./test -empty //./test/test1 //./test/test2 //./test/test1.txt
v. Search for files with permissions:
The find command is used to find all the files in the mentioned directory or sub-directory with the given permissions
find ./directory_name -perm permission_code Example: find ./test -perm 664
vi. Search text within multiple files:
find ./ -type f -name file_pattern -exec grep some_text {} \; Example: find ./ -type f -name "*.txt" -exec grep 'World' {} \; // Hello World
- Whereis to locate binary or source files for a command: The whereis command in Linux is used to locate the binary, source, and manual page files for a command. i.e, It is used to It is used to find executables of a program, its man pages and configuration files.
whereis command_name Example: whereis netstat //netstat: /bin/netstat /usr/share/man/man8/netstat.8.gz ( i.e, executable and location of its man page )
- Locate to find files: The locate command is used to find the files by name. This command is faster compared to find command because it searches database for the filename instead of searching your filesystem.
locate [OPTION] PATTERN Example: locate "*.txt" -n 10 // 10 file search results ending with .txt extension
# 10. SSH
SSH ( Secure Shell ) is a network protocol that enables secure remote connections between two systems.
- Connect remote machine using IP address or machine name: The remote server can be connected with local user name using either host name or IP address
ssh <host-name> or <ip-address> Example: ssh 192.111.66.100 ssh test.remoteserver.com
- Connect remote machine using username: It is also possible specify a user for an SSH connection.
ssh username@hostname_or_ip-address Example: ssh john@192.0.0.22 ssh john@test.remoteserver.com
- Connect remote machine using custom port By default, the SSH server listens for a connection on port 22. But you can also specify the custom port.
ssh <host-name> or <ip-address> -p port_number Example: ssh test.remoteserver.com -p 3322
- Generate SSH keys using keygen: SSH Keygen is used to generate a key pair which consists of public and private keys to improve the security of SSH connections.
ssh-keygen -t rsa
- Copying SSH keys to servers: For SSH authentication,
ssh-copy-id
command will be used to copy public key ( id_rsa.pub ) to server.
ssh-copy-id hostname_or_IP
- Copy a File Remotely over SSH: SCP tool is used to securely copy files over the SSH protocol.
scp fileName user@remotehost:destinationPath Example: scp test.txt test@10.0.0.64:/home/john/Desktop
- Edit SSH Config File SSH server options customized by editing the settings in
sshd_config
file.
sudo vim /etc/ssh/sshd_config
- Run commands on a remote server SSH commands can be executed on remote machine using the local machine.
ssh test.remoteserver.com mkdir NewDirectoryName // Creating directory on remote machine
- Restart SSH service: You need to restart the service in Linux after making changes to SSH configuration.
sudo ssh service restart (or) sudo sshd service restart
# 11. List of Basic SSH Commands
Sl.No. | Commands | Description |
---|---|---|
01. | ls | Show directory contents (list the names of files). |
02. | ls -a | List all files in a directory |
03. | ls -h | List files along with file sizes |
04. | ls *.html | list all files ending in .html |
05. | cd | Change directory (e.g. cd /var/www will put you in the www directory) |
06. | cd ~ | Go to the home folder |
07. | cd / | Go to the root directory |
08. | cd – | Go to the previous directory |
09. | cd .. | Move up one directory |
10. | mkdir | Create a new folder (e.g. mkdir myfoldername) |
11. | touch | Create a new file. |
12. | rm | Delete a file (e.g. rm filename.html) |
13. | rmdir | Delete a folder (e.g. rmdir foldername) |
14. | cat | Show the contents of a file (e.g. cat filename.html) |
15. | pwd | Show current directory (full path to where you are right now). |
16. | cp | Copy a file (e.g. cp index.html /mydirectory/index.html) |
17. | mv | Move a file (e.g. mv index.html /mydirectory/index.html) |
18. | grep | Search for a string (e.g. grep “word” index.html). Searches for “word” in the index.html file |
19. | find | Search files and directories. |
20. | vi/nano | Text editors. |
21. | history | Show last 50 used commands. |
22. | clear | Clear the terminal screen. |
23. | tar | Create & Unpack compressed archives. |
24. | wget | Download files and store them in your current directory (e.g. wget https://website.com/filename.ext) |
25. | du | Get file size. |
26. | vim | Open or create a file with the Vim text editor (e.g. vim filename.html). |
28. | nano | Open or create a file with the nano text editor (e.g. nano filename.html) |
29. | zip | Compress a folder (e.g. zip -r folder.zip folder). Takes “folder” and compresses it as a file called “folder.zip” |
30. | unzip | Decompresses a folder (e.g. unzip folder.zip) |
31. | chmod | Change a file’s permissions (e.g. chmod 604 folder). Use this Unix permissions calculator to determine which chmod command you should be using |
32. | netstat | Display network connections |
33. | free-m | Display your machine’s current memory usage |
34. | exit | Exit the remote server and return to your local machine SSH Keys |
35. | cat filename.txt | cat the contents of filename.txt to your screen |
36. | tail | like cat, but only reads the end of the file |
37. | tail /var/log/messages | see the last 20 (by default) lines of /var/log/message |
38. | tail -f /var/log/messages | watch the file continuously, while it’s being updat |
39. | tail -200 /var/log/messages | print the last 200 lines of the file to the screen |
40. | more | like cat, but opens the file one screen at a time rather than all at once |
41. | more /etc/userdomains | browse through the userdomains file. |
42. | pico | friendly, easy to use file editor |
43. | pico /home/burst/public_html/index.html | edit the index page for the user’s website. |
44. | vi | another editor, tons of features |
45. | vi /home/burst/public_html/index.html | edit the index page for the user’s website. |
46. | grep root /etc/passwd | shows all matches of root in /etc/passwd |
47. | grep -v root /etc/passwd | shows all lines that do not match root |
48. | touch /home/burst/public_html/404.html | create an empty file called 404.html in the directory /home/burst/public_html/ |
49. | ln | create’s “links” between files and directories |
50. | ln -s /home/username/tmp/webalizer webstats | Now you can display http://www.yourdomain.com/webstats to show your webalizer stats online. You can delete the symlink (webstats) and it will not delete the original stats on the server. |
51. | rm filename.txt | deletes filename.txt, will more than likely ask if you really want to delete it |
52. | rm -f filename.txt | deletes filename.txt, will not ask for confirmation before deleting. |
53. | rm -rf tmp/ | recursively deletes the directory tmp, and all files in it, including subdirectories. |
54. | last | shows who logged in and when |
55. | last -20 | shows only the last 20 logins |
56. | last -20 -a | shows last 20 logins, with the hostname in the last field |
57. | w | shows who is currently logged in and where they are logged in from. |
58. | netstat | shows all current network connections. |
59. | netstat -an | shows all connections to the server, the source and destination ips and ports. |
60. | netstat -rn | shows routing table for all ips bound to the server. |
61. | top | shows live system processes in a nice table, memory information, uptime and other useful info. |
62. | ps | ps is short for process status, which is similar to the top command. It’s used to show currently running processes and their PID. |
63. | ps U username | shows processes for a certain user |
64. | ps aux | shows all system processes |
65. | ps aux –forest | shows all system processes like the above but organizes in a hierarchy that’s very useful! |
66. | file | attempts to guess what type of file a file is by looking at it’s content. |
67. | file * | prints out a list of all files/directories in a directory |
68. | du | shows disk usage. |
69. | du -sh | shows a summary, in human-readble form, of total disk space used in the current directory, including subdirectories. |
70. | du -sh * | same thing, but for each file and directory. helpful when finding large files taking up space. |
71. | wc | word count |
72. | wc -l filename.txt | tells how many lines are in filename.txt |
73. | cp filename filename.backup | copies filename to filename.backup |
74. | cp -a /home/burst/new_design/* /home/burst/public_html/ | copies all files, retaining permissions form one directory to another. |
75. | find * -type d | xargs -i cp –verbose php.ini {} |
76. | kill | terminate a system process |
77. | kill -9 PID EG | kill -9 431 |
78. | kill PID EG | kill 10550 |
Editing Text
- Change word: Change word/part of word to right of cursorcw
- Change line Change entire linecc
- Change line from specific character Change from cursor to end of lineC
Deleting Text
- Deleting One Character: Position the cursor over the character to be deleted and type xx X //To delete one character before the cursor
- Deleting a Word: Position the cursor at the beginning of the word and type dwdw
- Deleting a Line: Position the cursor anywhere on the line and type dd.dd
Cut, Copy & Paste
Copy, Cut and Paste operations can be done in either Normal or visual Mode.
Exiting
These commands are used to exit from the file. ```cmd :w # Write (save) the file, but don't exit :wq # Write (save) and quit :wq! # Force write (save) and quit :q # Quit, but it fails if anything has changed :q! # Quit and throw away for any changes
# 12. Vi Editor
Vi editor is the most popular text editor from the early days of Unix. Whereas Vim ( Vi IMproved ) is an improved version of vi editor to be used in CLI ( command line interface ) for mainly text editing tasks in many configuration files. Some of the other alternatives are Elvis, Nvi, Nano, Joe, and Vile. It has two main operation modes,
- Command Mode: It allows the entry of commands to manipulate text.
- Entry mode ( Or Insert mode ): It allows typed characters on the keyboard into the current file.
1. Start with Vi Editor
You can create a new file or open an existing file using vi filename
command.
vi <filename_NEW> or <filename_EXISTING> // Create a new file or open an existing file Example: vi first.txt
Let’s see how do you create file, enter the content and leave the CLI by saving the changes.
- Create a new file named
first.txt
- Press
i
to enter the insert mode - Enter the text “Hello World!”
- Save the text and exit by pressing
:wq!
command - Check the entered text
2. Cursor movement
These commands will be used in Command mode.
Move cursor
You can use arrow keys ( left, right, up and down ) to move the cursor on the terminal. But you can also other keys for this behavior.
h # Move left j # Move down k # Move up l # Move right
Jump one word
These commands used to jump one word at a time
w # Jump forwards to the start of a word W # Jump forwards to the start of a WORD e # Jump forwards to the start of a word E # Jump forwards to the start of a WORD b # Jump backwords to the start of a word B # Jump backwords to the start of a WORD
Jump to start or end of a line or next line
These commands used to jump starting or ending of a line or a next line.
^ # Jump to the start of a current line $ # Jump to the end of a current line return # Jump to the start of a next line
Move sides
These commands used to moves all sides of the screen
Backspace # Move cursor one character to the left Spacebar # Move cursor one character to the right H ( High ) # Move cursor to the top of the screen M ( Middle ) # Move cursor to the middle of the screen L ( Low ) # Move cursor to the bottom of the screen
Paging and Scrolling
Paging is used to moves the cursor up or down through the text a full screen at a time. Whereas Scrolling happens line by line.
Ctrl + f # move forward one full screen Ctrl + b # move backward one full screen Ctrl + d # move forward half a screen Ctrl + u # move backward half a screen
Inserting Text
These commands places vi in entry mode from command mode. First, you need to be in command mode to use the below commands.
Insert
i # Insert text to the left of the cursor I # Insert text at the beginning of a line ESC # Exit insert mode
Append
a # Insert ( or Append ) text to the right of the cursor A # Insert ( or Append ) text at the end of a line
Open a line
o # Open a line below the current cursor position O # open a line above the current cursor position
Editing Text
- Change word: Change word/part of word to right of cursor
cw
Change line Change entire line
cc
Change line from specific character Change from cursor to end of line
c
Deleting Text
- Deleting One Character: Position the cursor over the character to be deleted and type x
x X //To delete one character before the cursor
Deleting a Word: Position the cursor at the beginning of the word and type dw
dw
Deleting a Line: Position the cursor anywhere on the line and type dd.
dd
Cut, Copy & Paste
Copy, Cut and Paste operations can be done in either Normal or visual Mode.
- Normal mode: This mode appears on click of
Esc
key.Copy There are various copy or yank commands based on amount of text to be copied. They
character is used to perform this operation.
i. Copy an entire line: Just place the cursor at the beginning of the line and typeyy
yy
ii.Copy three lines: Just place the cursor from where to start copying and type 3yy
3yy
iii. Copy word with trailing whitespace: Place the cursor at the beginning of the word and type yaw
yaw
iv. Copy word without trailing whitespace: Place the cursor at the beginning of the word and type yiw
.
yiw
v. Copy right of the cursor: Copy text right of the cursor to the end of line using y$
command
y$
vi.Copy left of the cursor: Copy text left of the cursor to the end of line using y^
command
y^
vii. Copy text between the cursor and character: Copy text between the cursor and specified character.
ytx ( Copy until x and x is excluded ) yfx ( Copy until x and x is included )
Cut There are various cutting or deleting commands based on amount of text to be deleted. The d
character is used to perform this operation.
i. Cut entire line: Cut the entire line where the cursor is located
dd
ii.Cut three lines: Cut the three lines starting from the place where cursor is located
3dd
iii.Cut right of the cursor: Cut the text from the right of the cursor till the end of line
d$
iii.Cut left of the cursor: Cut the text from the left of the cursor till the beginning of line
d^
Paste This operation is performed using p
command to paste the selected text
p
- Visual Mode In this mode, first select the text using below keys
- v ( lowercase ): To select individual characters
- V ( uppercase ): To select the entire line
- Ctrl+v: To select by block
Exiting
These commands are used to exit from the file. ```cmd :w # Write (save) the file, but don't exit :wq # Write (save) and quit :wq! # Force write (save) and quit :q # Quit, but it fails if anything has changed :q! # Quit and throw away for any changes ```
# 13. Process Management
Sl.No. | Commands | Description |
---|---|---|
01. | ps | display your currently active processes |
02. | top | display all running processes |
03. | kill pid | kill process id pid |
04. | killall proc | kill all processes named proc * |
05. | bg | lists stopped or background jobs; resume a stopped job in the background |
06. | fg | brings the most recent job to foreground |
07. | fg n | brings job n to the foreground |
# 14. SSH
- ssh user@host – connect to host as user
- ssh -p port user@host – connect to host on port port as user
- ssh-copy-id user@host – add your key to host for user to enable a keyed or passwordless login
Searching
- grep pattern files – search for pattern in files
- grep -r pattern dir – search recursively for pattern in dir
- command | grep pattern – search for pattern in the output of command
- locate file – find all instances of file
System Info
Sl.No. | Commands | Description |
---|---|---|
01. | date | show the current date and time |
02. | cal | show this month’s calendar |
03. | uptime | show current uptime |
04. | w | display who is online |
05. | whoami | who you are logged in as |
06. | finger user | display information about user |
07. | uname -a | show kernel information |
08. | cat /proc/cpuinfo | cpu information |
09. | cat /proc/meminfo | memory information |
10. | man command | show the manual for command |
11. | df | show disk usage |
12. | du | show directory space usage |
13. | free | show memory and swap usage |
14. | whereis app | show possible locations of app |
15. | which app | show which app will be run by default |
Compression
Sl.No. | Commands | Description |
---|---|---|
01. | tar cf file.tar files | create a tar named file.tar containing files |
02. | tar xf file.tar | extract the files from file.tar |
03. | tar czf file.tar.gz files | create a tar with Gzip compression |
04. | tar xzf file.tar.gz | extract a tar using Gzip |
05. | tar cjf file.tar.bz2 | create a tar with Bzip2 compression |
06. | tar xjf file.tar.bz2 | extract a tar using Bzip2 |
07. | gzip file | compresses file and renames it to file.gz |
08. | gzip -d file.gz | decompresses file.gz back to file |
Network
- ping host – ping host and output results
- whois domain – get whois information for domain
- dig domain – get DNS information for domain
- dig -x host – reverse lookup host
- wget file – download file
- wget -c file – continue a stopped download
Installation
- dpkg -i pkg.deb – install a package (Debian)
- rpm -Uvh pkg.rpm – install a package (RPM)
Install from source
- ./configure
- make
- make install
Shortcuts
- Ctrl+C – halts the current command
- Ctrl+Z – stops the current command, resume with
- fg in the foreground or bg in the background
- Ctrl+D – log out of current session, similar to exit
- Ctrl+W – erases one word in the current line
- Ctrl+U – erases the whole line
- Ctrl+R – type to bring up a recent command
- !! – repeats the last command
- exit – log out of current session
Command History
!! # Run the last command touch foo.sh chmod +x !$ # !$ is the last argument of the last command i.e. foo.sh
Navigating Directories
pwd # Print current directory path ls # List directories ls -a|--all # List directories including hidden ls -l # List directories in long form ls -l -h|--human-readable # List directories in long form with human readable sizes ls -t # List directories by modification time, newest first stat foo.txt # List size, created and modified timestamps for a file stat foo # List size, created and modified timestamps for a directory tree # List directory and file tree tree -a # List directory and file tree including hidden tree -d # List directory tree cd foo # Go to foo sub-directory cd # Go to home directory cd ~ # Go to home directory cd - # Go to last directory pushd foo # Go to foo sub-directory and add previous directory to stack popd # Go back to directory in stack saved by `pushd`
Creating Directories
mkdir foo # Create a directory mkdir foo bar # Create multiple directories mkdir -p|--parents foo/bar # Create nested directory mkdir -p|--parents {foo,bar}/baz # Create multiple nested directories mktemp -d|--directory # Create a temporary directory
Moving Directories
cp -R|--recursive foo bar # Copy directory mv foo bar # Move directory rsync -z|--compress -v|--verbose /foo /bar # Copy directory, overwrites destination rsync -a|--archive -z|--compress -v|--verbose /foo /bar # Copy directory, without overwriting destination rsync -avz /foo username@hostname:/bar # Copy local directory to remote directory rsync -avz username@hostname:/foo /bar # Copy remote directory to local directory
Deleting Directories
rmdir foo # Delete non-empty directory rm -r|--recursive foo # Delete directory including contents rm -r|--recursive -f|--force foo # Delete directory including contents, ignore nonexistent files and never prompt
Creating Files
touch foo.txt # Create file or update existing files modified timestamp touch foo.txt bar.txt # Create multiple files touch {foo,bar}.txt # Create multiple files touch test{1..3} # Create test1, test2 and test3 files touch test{a..c} # Create testa, testb and testc files mktemp # Create a temporary file
Standard Output, Standard Error and Standard Input
echo "foo" > bar.txt # Overwrite file with content echo "foo" >> bar.txt # Append to file with content ls exists 1> stdout.txt # Redirect the standard output to a file ls noexist 2> stderror.txt # Redirect the standard error output to a file ls 2>&1 out.txt # Redirect standard output and error to a file ls > /dev/null # Discard standard output and error read foo # Read from standard input and write to the variable foo
Moving Files
cp foo.txt bar.txt # Copy file mv foo.txt bar.txt # Move file rsync -z|--compress -v|--verbose /foo.txt /bar # Copy file quickly if not changed rsync z|--compress -v|--verbose /foo.txt /bar.txt # Copy and rename file quickly if not changed
Deleting Files
rm foo.txt # Delete file rm -f|--force foo.txt # Delete file, ignore nonexistent files and never prompt
Reading Files
cat foo.txt # Print all contents less foo.txt # Print some contents at a time (g - go to top of file, SHIFT+g, go to bottom of file, /foo to search for 'foo') head foo.txt # Print top 10 lines of file tail foo.txt # Print bottom 10 lines of file open foo.txt # Open file in the default editor wc foo.txt # List number of lines words and characters in the file
Finding Files
Find binary files for a command.
type wget # Find the binary which wget # Find the binary whereis wget # Find the binary, source, and manual page files
locate
uses an index and is fast.
updatedb # Update the index locate foo.txt # Find a file locate --ignore-case # Find a file and ignore case locate f*.txt # Find a text file starting with 'f'
find
doesn’t use an index and is slow.
find /path -name foo.txt # Find a file find /path -iname foo.txt # Find a file with case insensitive search find /path -name "*.txt" # Find all text files find /path -name foo.txt -delete # Find a file and delete it find /path -name "*.png" -exec pngquant {} # Find all .png files and execute pngquant on it find /path -type f -name foo.txt # Find a file find /path -type d -name foo # Find a directory find /path -type l -name foo.txt # Find a symbolic link find /path -type f -mtime +30 # Find files that haven't been modified in 30 days find /path -type f -mtime +30 -delete # Delete files that haven't been modified in 30 days
Find in Files
grep 'foo' /bar.txt # Search for 'foo' in file 'bar.txt' grep 'foo' /bar -r|--recursive # Search for 'foo' in directory 'bar' grep 'foo' /bar -R|--dereference-recursive # Search for 'foo' in directory 'bar' and follow symbolic links grep 'foo' /bar -l|--files-with-matches # Show only files that match grep 'foo' /bar -L|--files-without-match # Show only files that don't match grep 'Foo' /bar -i|--ignore-case # Case insensitive search grep 'foo' /bar -x|--line-regexp # Match the entire line grep 'foo' /bar -C|--context 1 # Add N line of context above and below each search result grep 'foo' /bar -v|--invert-match # Show only lines that don't match grep 'foo' /bar -c|--count # Count the number lines that match grep 'foo' /bar -n|--line-number # Add line numbers grep 'foo' /bar --colour # Add colour to output grep 'foo\|bar' /baz -R # Search for 'foo' or 'bar' in directory 'baz' grep --extended-regexp|-E 'foo|bar' /baz -R # Use regular expressions egrep 'foo|bar' /baz -R # Use regular expressions
Replace in Files
sed 's/fox/bear/g' foo.txt # Replace fox with bear in foo.txt and output to console sed 's/fox/bear/gi' foo.txt # Replace fox (case insensitive) with bear in foo.txt and output to console sed 's/red fox/blue bear/g' foo.txt # Replace red with blue and fox with bear in foo.txt and output to console sed 's/fox/bear/g' foo.txt > bar.txt # Replace fox with bear in foo.txt and save in bar.txt sed 's/fox/bear/g' foo.txt -i|--in-place # Replace fox with bear and overwrite foo.txt
Symbolic Links
ln -s|--symbolic foo bar # Create a link 'bar' to the 'foo' folder ln -s|--symbolic -f|--force foo bar # Overwrite an existing symbolic link 'bar' ls -l # Show where symbolic links are pointing
Compressing Files
zip
Compresses one or more files into *.zip files.
zip foo.zip /bar.txt # Compress bar.txt into foo.zip zip foo.zip /bar.txt /baz.txt # Compress bar.txt and baz.txt into foo.zip zip foo.zip /{bar,baz}.txt # Compress bar.txt and baz.txt into foo.zip zip -r|--recurse-paths foo.zip /bar # Compress directory bar into foo.zip
gzip
Compresses a single file into *.gz files.
gzip /bar.txt foo.gz # Compress bar.txt into foo.gz and then delete bar.txt gzip -k|--keep /bar.txt foo.gz # Compress bar.txt into foo.gz
tar -c
Compresses (optionally) and combines one or more files into a single *.tar, *.tar.gz, *.tpz or *.tgz file.
tar -c|--create -z|--gzip -f|--file=foo.tgz /bar.txt /baz.txt # Compress bar.txt and baz.txt into foo.tgz tar -c|--create -z|--gzip -f|--file=foo.tgz /{bar,baz}.txt # Compress bar.txt and baz.txt into foo.tgz tar -c|--create -z|--gzip -f|--file=foo.tgz /bar # Compress directory bar into foo.tgz
Decompressing Files
unzip
unzip foo.zip # Unzip foo.zip into current directory
gunzip
gunzip foo.gz # Unzip foo.gz into current directory and delete foo.gz gunzip -k|--keep foo.gz # Unzip foo.gz into current directory
tar -x
tar -x|--extract -z|--gzip -f|--file=foo.tar.gz # Un-compress foo.tar.gz into current directory tar -x|--extract -f|--file=foo.tar # Un-combine foo.tar into current directory
Disk Usage
df # List disks, size, used and available space df -h|--human-readable # List disks, size, used and available space in a human readable format du # List current directory, subdirectories and file sizes du /foo/bar # List specified directory, subdirectories and file sizes du -h|--human-readable # List current directory, subdirectories and file sizes in a human readable format du -d|--max-depth # List current directory, subdirectories and file sizes within the max depth du -d 0 # List current directory size
Memory Usage
free # Show memory usage free -h|--human # Show human readable memory usage free -h|--human --si # Show human readable memory usage in power of 1000 instead of 1024 free -s|--seconds 5 # Show memory usage and update continuously every five seconds
Packages
apt update # Refreshes repository index apt search wget # Search for a package apt show wget # List information about the wget package apt install wget # Install the wget package apt remove wget # Removes the wget package apt upgrade # Upgrades all upgradable packages
Shutdown and Reboot
shutdown # Shutdown in 1 minute shutdown now "Cya later" # Immediately shut down shutdown +5 "Cya later" # Shutdown in 5 minutes shutdown --reboot # Reboot in 1 minute shutdown -r now "Cya later" # Immediately reboot shutdown -r +5 "Cya later" # Reboot in 5 minutes shutdown -c # Cancel a shutdown or reboot reboot # Reboot now reboot -f # Force a reboot
Identifying Processes
top # List all processes interactively htop # List all processes interactively ps all # List all processes pidof foo # Return the PID of all foo processes CTRL+Z # Suspend a process running in the foreground bg # Resume a suspended process and run in the background fg # Bring the last background process to the foreground fg 1 # Bring the background process with the PID to the foreground sleep 30 & # Sleep for 30 seconds and move the process into the background jobs # List all background jobs jobs -p # List all background jobs with their PID lsof # List all open files and the process using them lsof -itcp:4000 # Return the process listening on port 4000
Process Priority
Process priorities go from -20 (highest) to 19 (lowest).
nice -n -20 foo # Change process priority by name renice 20 PID # Change process priority by PID ps -o ni PID # Return the process priority of PID
Killing Processes
CTRL+C # Kill a process running in the foreground kill PID # Shut down process by PID gracefully. Sends TERM signal. kill -9 PID # Force shut down of process by PID. Sends SIGKILL signal. pkill foo # Shut down process by name gracefully. Sends TERM signal. pkill -9 foo # force shut down process by name. Sends SIGKILL signal. killall foo # Kill all process with the specified name gracefully.
Date & Time
date # Print the date and time date --iso-8601 # Print the ISO8601 date date --iso-8601=ns # Print the ISO8601 date and time time tree # Time how long the tree command takes to execute
Scheduled Tasks
* * * * * Minute, Hour, Day of month, Month, Day of the week
crontab -l # List cron tab crontab -e # Edit cron tab in Vim crontab /path/crontab # Load cron tab from a file crontab -l > /path/crontab # Save cron tab to a file * * * * * foo # Run foo every minute */15 * * * * foo # Run foo every 15 minutes 0 * * * * foo # Run foo every hour 15 6 * * * foo # Run foo daily at 6:15 AM 44 4 * * 5 foo # Run foo every Friday at 4:44 AM 0 0 1 * * foo # Run foo at midnight on the first of the month 0 0 1 1 * foo # Run foo at midnight on the first of the year at -l # List scheduled tasks at -c 1 # Show task with ID 1 at -r 1 # Remove task with ID 1 at now + 2 minutes # Create a task in Vim to execute in 2 minutes at 12:34 PM next month # Create a task in Vim to execute at 12:34 PM next month at tomorrow # Create a task in Vim to execute tomorrow
HTTP Requests
curl https://example.com # Return response body curl -i|--include https://example.com # Include status code and HTTP headers curl -L|--location https://example.com # Follow redirects curl -o|--remote-name foo.txt https://example.com # Output to a text file curl -H|--header "User-Agent: Foo" https://example.com # Add a HTTP header curl -X|--request POST -H "Content-Type: application/json" -d|--data '{"foo":"bar"}' https://example.com # POST JSON curl -X POST -H --data-urlencode foo="bar" http://example.com # POST URL Form Encoded wget https://example.com/file.txt . # Download a file to the current directory wget -O|--output-document foo.txt https://example.com/file.txt # Output to a file with the specified name
Network Troubleshooting
ping example.com # Send multiple ping requests using the ICMP protocol ping -c 10 -i 5 example.com # Make 10 attempts, 5 seconds apart ip addr # List IP addresses on the system ip route show # Show IP addresses to router netstat -i|--interfaces # List all network interfaces and in/out usage netstat -l|--listening # List all open ports traceroute example.com # List all servers the network traffic goes through mtr -w|--report-wide example.com # Continually list all servers the network traffic goes through mtr -r|--report -w|--report-wide -c|--report-cycles 100 example.com # Output a report that lists network traffic 100 times nmap 0.0.0.0 # Scan for the 1000 most common open ports on localhost nmap 0.0.0.0 -p1-65535 # Scan for open ports on localhost between 1 and 65535 nmap 192.168.4.3 # Scan for the 1000 most common open ports on a remote IP address nmap -sP 192.168.1.1/24 # Discover all machines on the network by ping'ing them
DNS
host example.com # Show the IPv4 and IPv6 addresses dig example.com # Show complete DNS information cat /etc/resolv.conf # resolv.conf lists nameservers
Hardware
lsusb # List USB devices lspci # List PCI hardware lshw # List all hardware
Terminal Multiplexers
Start multiple terminal sessions. Active sessions persist reboots. tmux
is more modern than screen
.
tmux # Start a new session (CTRL-b + d to detach) tmux ls # List all sessions tmux attach -t 0 # Reattach to a session screen # Start a new session (CTRL-a + d to detach) screen -ls # List all sessions screen -R 31166 # Reattach to a session exit # Exit a session
Secure Shell Protocol (SSH)
ssh hostname # Connect to hostname using your current user name over the default SSH port 22 ssh -i foo.pem hostname # Connect to hostname using the identity file ssh user@hostname # Connect to hostname using the user over the default SSH port 22 ssh user@hostname -p 8765 # Connect to hostname using the user over a custom port ssh ssh://user@hostname:8765 # Connect to hostname using the user over a custom port
Set default user and port in ~/.ssh/config
, so you can just enter the name next time:
$ cat ~/.ssh/config Host name User foo Hostname 127.0.0.1 Port 8765 $ ssh name
Secure Copy
scp foo.txt ubuntu@hostname:/home/ubuntu # Copy foo.txt into the specified remote directory
Bash Profile
- bash –
.bashrc
- zsh –
.zshrc
# Always run ls after cd function cd { builtin cd "$@" && ls } # Prompt user before overwriting any files alias cp='cp --interactive' alias mv='mv --interactive' alias rm='rm --interactive' # Always show disk usage in a human readable format alias df='df -h' alias du='du -h'
Bash Script
Variables
#!/bin/bash foo=123 # Initialize variable foo with 123 declare -i foo=123 # Initialize an integer foo with 123 declare -r foo=123 # Initialize readonly variable foo with 123 echo $foo # Print variable foo echo ${foo}_'bar' # Print variable foo followed by _bar echo ${foo:-'default'} # Print variable foo if it exists otherwise print default export foo # Make foo available to child processes unset foo # Make foo unavailable to child processes
Environment Variables
#!/bin/bash env # List all environment variables echo $PATH # Print PATH environment variable
Functions
#!/bin/bash greet() { local world = "World" echo "$1 $world" return "$1 $world" } greet "Hello" greeting=$(greet "Hello")
Exit Codes
#!/bin/bash exit 0 # Exit the script successfully exit 1 # Exit the script unsuccessfully echo $? # Print the last exit code
Conditional Statements
Boolean Operators
$foo
– Is true!$foo
– Is false
Numeric Operators
-eq
– Equals-ne
– Not equals-gt
– Greater than-ge
– Greater than or equal to-lt
– Less than-le
– Less than or equal to-e
foo.txt – Check file exists-z
foo – Check if variable exists
String Operators
=
– Equals==
– Equals-z
– Is null-n
– Is not null<
– Is less than in ASCII alphabetical order>
– Is greater than in ASCII alphabetical order
If Statements
#!/bin/bash if [[$foo = 'bar']]; then echo 'one' elif [[$foo = 'bar']] || [[$foo = 'baz']]; then echo 'two' elif [[$foo = 'ban']] && [[$USER = 'bat']]; then echo 'three' else echo 'four' fi
Inline If Statements
#!/bin/bash [[ $USER = 'rehan' ]] && echo 'yes' || echo 'no'
While Loops
#!/bin/bash declare -i counter counter=10 while [$counter -gt 2]; do echo The counter is $counter counter=counter-1 done
For Loops
#!/bin/bash for i in {0..10..2} do echo "Index: $i" done for filename in file1 file2 file3 do echo "Content: " >> $filename done for filename in *; do echo "Content: " >> $filename done
Case Statements
#!/bin/bash echo 'What's the weather like tomorrow?' read weather case $weather in sunny | warm ) echo 'Nice weather: ' $weather ;; cloudy | cool ) echo 'Not bad weather: ' $weather ;; rainy | cold ) echo 'Terrible weather: ' $weather ;; * ) echo 'Don't understand' ;; esac
The Linuc Basics is a github repository by Pradeep Kumar
Leave a Reply