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https://github.com/sudheerj/Linux-cheat-sheet

List of Linux commands
https://github.com/sudheerj/Linux-cheat-sheet

cheatsheet linux linuxcommand ubuntu vim

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List of Linux commands

Host: GitHub
URL: https://github.com/sudheerj/Linux-cheat-sheet
Owner: sudheerj
Created: 2019-08-01T15:54:47.000Z (about 5 years ago)
Default Branch: master
Last Pushed: 2023-12-26T00:38:03.000Z (9 months ago)
Last Synced: 2024-07-27T18:57:07.036Z (about 2 months ago)
Topics: cheatsheet, linux, linuxcommand, ubuntu, vim
Homepage:
Size: 168 KB
Stars: 459
Watchers: 9
Forks: 215
Open Issues: 0
Metadata Files:
- Readme: README.md

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README

# Linux-cheat-sheet

> Click :star:if you like the project. Pull Request are highly appreciated. Follow me [@SudheerJonna](https://twitter.com/SudheerJonna) for technical updates.

### Table of Contents

---

| No. | Topic |
| --- | ----------------------------------------------------------------------- |
| 1 | [**User information**](#user-information) |
| 2 | [**File and directory commands**](#file-and-directory-commands) |
| 3 | [**File permissions**](#file-permissions) |
| 4 | [**Networking**](#networking) |
| 5 | [**Installing packages**](#installing-packages) |
| 6 | [**Disk usage**](#disk-usage) |
| 7 | [**System and Hardware information**](#system-and-hardware-information) |
| 8 | [**Search Files**](#search-files) |
| 9 | [**SSH**](#ssh) |
| 10 | [**Vi/Vim-commands**](#vi/vim-commands) |
| 11 | [**Top/TaskManager Command**](#Top-Command) |
| 12 | [**Kill Command**](#Kill-Command) |
| 13 | [**History Command**](#History-Command) |
| 14 | [**Curl Command**](#Curl-Command) |

### User Information

1. **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.

1. Login name of the user
2. User terminal
3. Date & Time of login
4. Remote host name of the user

```bash
$ who
sudheer :0 2019-08-04 01:21 (:0)
```

2. **whoami:** It display the system’s username

```bash
$ whoami
sudheer
```

3. **id:** It display the user identification(the real and effective user and group IDs) information

```bash
$ 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)
```
4. **groups:** This command is used to display all the groups for which the user belongs to.

```bash
$ group
sj: sj, adm, cdrom, sudo, dip, plugdev, lpadmin, lxd, sambashare
```

5. **finger:** Used to check the information of any currently logged in users. i.e, It displays users login time, tty (name), idle time, home directory, shell name etc.

```bash
$ finger
Login Name Tty Idle Login Time Office Office Phone
sj sj *:0 Aug 28 01:27 (:0)
```

This may not be available by default in many linux machines. In this case, you need to install it manually.

```bash
$ sudo apt install finger
```
6. **users:** Displays usernames of all users currently logged on the system.

```bash
$ users
sj
```

7. **grep:** It is a powerful pattern searching tool to find information about a specific user from the system accounts file: /etc/passwd.

```bash
$ grep -i sj /etc/passwd
sj:x:1000:1000:sj,,,:/home/sj:/bin/bash
```

8. **W Command:** It(W) is a command-line utility that displays information about currently logged in users and what each user is doing.

```bash
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
```

9. **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.

```bash
last [options] [username...] [tty...]

Example:

last
sj :0 :0 Fri Aug 28 01:27 gone - no logout
reboot system boot 5.4.0-29-generic Fri Aug 28 01:27 still running
sj :0 :0 Wed Jul 29 11:46 - crash (29+13:40)
reboot system boot 5.4.0-29-generic Wed Jul 29 11:45 still running
sj :0 :0 Thu May 14 21:04 - crash (75+14:41)
reboot system boot 5.4.0-29-generic Thu May 14 21:03 still running

wtmp begins Thu May 14 21:03:56 2020
```

10. **lastlog:** The `lastlog` command is used to find the details of a recent login of all users or of a given user.

```cmd
$ lastlog

Username Port From Latest
root **Never logged in**
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**
```

**[⬆ Back to Top](#table-of-contents)**

### File and directory commands

1. **pwd** The pwd(Present Working Directory) command is used to print the name of the present/current working directory starting from the root.
```bash
$ pwd
/home/sj/Desktop/Linux
```

2. **ls**: The `ls` command is used to list files or directories. It also accepts some flags or options that changes how files or directories are listed in your terminal.

```bash
Syntax:
ls [flags] [directory]

Example:
$ ls
bin dev lib libx32 mnt

//Listing files & directories with time in a rever order
$ ls -ltr
drwxr-xr-x 2 sj sj 4096 May 14 2020 Videos
drwxr-xr-x 2 sj sj 4096 May 14 2020 Templates
drwxr-xr-x 2 sj sj 4096 May 14 2020 Public

//Home directory
$ ls ~
Desktop Downloads Pictures Sudheer test test.txt
Documents Music Public Templates test1 Videos
```

Below are the list of possible options for `ls` command,

```cmd
-a Show all (including hidden)
-R Recursive list
-r Reverse order
-t Sort by last modified
-S Sort by file size
-l Long listing format
-1 One file per line
-m Comma-separated output
-Q Quoted output
```

3. **mkdir** The mkdir(make directory) command allows users to create directories or folders.

```bash
$ mkdir ubuntu
$ ls
ubuntu
```

The option '-p' is used to create multiple directories or parent directories at once.

```bash
$ mkdir -p dir1/dir2/dir3
$ cd dir1/dir2/dir3
~/Desktop/Linux/dir1/dir2/dir3$
```

4. **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.

1. Remove empty directory:

```bash
rmdir FolderName
```

2. Remove multiple directories:

```bash
rmdir FolderName1 FolderName2 FolderName3
```

3. Remove non-empty directories:

```bash
rmdir FolderName1 --ignore-fail-on-non-empty
```

4. Remove entire directory tree. This command is similar to `rmdir a/b/c a/b a`:

```bash
rmdir -p a/b/c
```

5. **rm**: The rm(remove) command is used to remove objects such as files, directories, symbolic links etc from the file system.
1. Remove file: The rm command is used to remove or delete a file
```bash
rm file_name
```
2. Remove file forcefully: The rm command with -f option is used for removal of file without prompting for confirmation.
```bash
rm -f filename
```
3. Remove directory: The rm command with -r option is used to remove the directory and its contents recursively.
```bash
rm -r myDir
```
4. Remove directory forcefully: The rm command with -rf option is used to forcefully remove directory recursively.
```bash
rm -rf myDir
```
6. **touch**: The touch command is is used to create, change and modify timestamps of a file without any content.
1. **Create a new file:** You can create a single file at a time using touch command. The file created is an empty file.
```bash
touch file_name
```
2. **Create multiple files:** You can create the multiple numbers of files at the same time.
```bash
touch file1_name file2_name file3_name
```
3. **Change access time:** The touch command with `a` option is used to change the access time of a file.
```bash
touch -a file_name
```
4. **Change modification time:** The touch command with `m` option is used to change the modified time.
```bash
touch -m file_name
```
5. **Use timestamp of other file:** The touch command with `r` option is used to get timestamp of another file.
```bash
touch -r file2 file1
```

In the above example, we get the timestamp of file1 for file2.

6. **Create file with Specific time:** The touch command with 't' option is used to create a file with specified time.
```bash
touch -t 1911010000 file_name
```
7. **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.
```bash
$ cat [OPTION] [FILE]...
```
1. **Create a file:** Used to create a file with specific name, content and press exit using `CTRL + D`
```bash
cat > file_name1.txt
Hello, How are you?
```
2. **View file contents:** You can view contents of a single or more files by mentioning the filenames.

```bash
cat file_name1 file_name2
```
3. **More & Less options:** If a file having a large number of content that won’t fit in the output terminal then `more` & `less` options can be used to indiate additional content.

```bash
cat file_name1.txt | more
cat file_name1.txt | less
```

**[⬆ Back to Top](#table-of-contents)**

### File permissions
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,

1. **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

2. **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

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.

```cmd
chmod [reference][operator][mode] file...

Example
chmod ugo-rwx test.txt
```

There are 2 ways to use this command,

1. **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,

```cmd
chmode 764 test.txt
```

2. **Symbolic mode:**
In the symbolic mode, you can modify permissions of a specific owner unlike absolute mode.

The owners are represented as below,

| Owner | Description |
| ----- | ----- |
| u | user/owner |
| g | group |
| o | other |
| a | all |

and the list of mathematical symbols to modify the file permissions as follows,

| Operator | Description |
| ------------- | ----- |
| + | 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.

```cmd
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

```cmd
chgrp group_name filename

Example:
sudo chgrp Administrator test.txt
```

**[⬆ Back to Top](#table-of-contents)**

### Networking

1. **Display network information:** `ifconfig` command is used to display all network information(ip address, ports etc)

```cmd
ifconfig -a
```

2. **Test connection to a remote machine:** Send an echo request to test connection of a remote machine.

```cmd
ping or hostname

Example:
ping 10.0.0.11
```

3. **Show IP Address:** Display ip address of a currennt machine

```cmd
hostname -I
(OR)
ip addr show
```

4. **Active ports:** Shows active or listening ports

```cmd
netstat -pnltu
```

5. **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.

```cmd
whois [domain]

Example:
whois google.com
```

**[⬆ Back to Top](#table-of-contents)**

### Installing packages

1. **Install package:**

```cmd
yum install package_name
```

2. **Package description:**
The info command is used to display brief details about a package.

```cmd
yum info package_name
```

3. **Uninstall package:**
The remove command is used to remove or uninstall package name.
```cmd
yum remove package_name
```
4. **Install package from local file:**

It is also possible to install package from local file named package_name.rpm.

```cmd
rpm -i package_name.rpm
```

5. **Install from source code:**

```cmd
tar zxvf sourcecode.tar.gz
cd sourcecode
./configure
make
make install
```

**[⬆ Back to Top](#table-of-contents)**

### Disk usage

1. **Synopsis:** `du` command is used to check the information of disk usage of files and directories on a machine

```cmd
du [OPTION]... [FILE]...
```

2. **Disk usage of a directory:** To find out the disk usage summary of a /home/ directory tree and each of its sub directories

```cmd
du /home/
```

3. **Disk usage in human readable format:** To find out the disk usage in human readable format

```cmd
du -h /home/
```

4. **Total disk usage of a directory:** To find out the total disk usage

```cmd
du -sh /home/
```

5. **Total disk usage of all files and directories:** To find out the total disk usage of files and directories

```cmd
du -ah /home/
```

6. **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

```cmd
du -ah --max-depth 2 /home/
```

7. **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.

```cmd
du -ah --exclude="*.txt" /home/
```

8. **Help:** This command gives information about `du`

```cmd
du --help
```

**[⬆ Back to Top](#table-of-contents)**

### System and Hardware information

1. **Print all information**: `uname` is mainly used to print system information.

```bash
$ uname -a
```

2. **Print kernel name**:

```bash
$ uname -s
```

3. **Print kernel release**:

```bash
$ uname -r
```

4. **Print Architecture**:

```bash
$ uname -m
```

5. **Print Operating System**:

```bash
$ uname -o
```

**[⬆ Back to Top](#table-of-contents)**

### Search Files

1. **Pattern search:**
The `grep` command is used to search patterns in files.

```cmd
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
```

2. **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:**

```cmd
find ./directory_name -name file_name

Example:
find ./test -name test.txt // ./test/test.txt
```

ii. **Search file with pattern:**

```cmd
find ./directory_name -name file_pattern

Example:
find ./test -name *.txt // ./test/test.txt
```

iii. **Search file with executable action:**

```cmd
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.

```cmd
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

```cmd
find ./directory_name -perm permission_code

Example:
find ./test -perm 664
```

vi. **Search text within multiple files:**

```cmd
find ./ -type f -name file_pattern -exec grep some_text {} \;

Example:
find ./ -type f -name "*.txt" -exec grep 'World' {} \; // Hello World
```

3. **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.

```cmd
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)
```

4. **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.

```cmd
locate [OPTION] PATTERN

Example:
locate "*.txt" -n 10 // 10 file search results ending with .txt extension
```

**[⬆ Back to Top](#table-of-contents)**

### SSH

SSH (Secure Shell) is a network protocol that enables secure remote connections between two systems.

1. **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

```cmd
ssh or

Example:
ssh 192.111.66.100
ssh test.remoteserver.com
```

2. **Connect remote machine using username:** It is also possible specify a user for an SSH connection.

```cmd
ssh username@hostname_or_ip-address

Example:
ssh [email protected]
ssh [email protected]
```

3. **: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.

```cmd
ssh or -p port_number

Example:
ssh test.remoteserver.com -p 3322
```

4. **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.

```cmd
ssh-keygen -t rsa
```

5. **Copying SSH keys to servers:** For SSH authentication, `ssh-copy-id` command will be used to copy public key(id_rsa.pub) to server.

```cmd
ssh-copy-id hostname_or_IP
```

6. **Copy a File Remotely over SSH:** SCP tool is used to securely copy files over the SSH protocol.

```cmd
scp fileName user@remotehost:destinationPath

Example:
scp test.txt [email protected]:/home/john/Desktop
```

7. **Edit SSH Config File** SSH server options customized by editing the settings in `sshd_config` file.

```cmd
sudo vim /etc/ssh/sshd_config
```

8. **Run commands on a remote server** SSH commands can be executed on remote machine using the local machine.

```cmd
ssh test.remoteserver.com mkdir NewDirectoryName // Creating directory on remote machine
```

9. **Restart SSH service:** You need to restart the service in Linux after making changes to SSH configuration.

```cmd
sudo ssh service restart
(or)
sudo sshd service restart
```

**[⬆ Back to Top](#table-of-contents)**

### Vi/Vim-commands

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,

1. **Command Mode:** It allows the entry of commands to manipulate text.
2. **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.

```cmd
vi or // 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.

1. Create a new file named `first.txt`
2. Press `i` to enter the insert mode
3. Enter the text "Hello World!"
4. Save the text and exit by pressing `:wq!` command
5. 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.

```cmd
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

```cmd
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.

```cmd
^ # 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

```cmd
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.

```cmd
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

```cmd
i # Insert text to the left of the cursor
I # Insert text at the beginning of a line
ESC # Exit insert mode
```

###### Append

```cmd
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

```cmd
o # Open a line below the current cursor position
O # open a line above the current cursor position
```

##### Editing Text

1. **Change word:** Change word/part of word to right of cursor

```cmd
cw
```

2. **Change line** Change entire line

```cmd
cc
```

3. **Change line from specific character** Change from cursor to end of line

```cmd
C
```

##### Deleting Text

1. **Deleting One Character:** Position the cursor over the character to be deleted and type x

```cmd
x
X //To delete one character before the cursor
```
2. **Deleting a Word:** Position the cursor at the beginning of the word and type dw

```cmd
dw
```
3. **Deleting a Line:** Position the cursor anywhere on the line and type dd.

```cmd
dd
```

##### Cut, Copy & Paste

Copy, Cut and Paste operations can be done in either Normal or visual Mode.

1. **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. The `y` character is used to perform this operation.

i. Copy an entire line: Just place the cursor at the beginning of the line and type `yy`

```cmd
yy
```

ii.Copy three lines: Just place the cursor from where to start copying and type `3yy`

```cmd
3yy
```

iii. Copy word with trailing whitespace: Place the cursor at the beginning of the word and type `yaw`

```cmd
yaw
```

iv. Copy word without trailing whitespace: Place the cursor at the beginning of the word and type `yiw`.

```cmd
yiw
```

v. Copy right of the cursor: Copy text right of the cursor to the end of line using `y$` command

```cmd
y$
```

vi.Copy left of the cursor: Copy text left of the cursor to the end of line using `y^` command

```cmd
y^
```

vii. Copy text between the cursor and character: Copy text between the cursor and specified character.

```cmd
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

```cmd
dd
```

ii.Cut three lines: Cut the three lines starting from the place where cursor is located

```cmd
3dd
```

iii.Cut right of the cursor: Cut the text from the right of the cursor till the end of line

```cmd
d$
```

iii.Cut left of the cursor: Cut the text from the left of the cursor till the beginning of line

```cmd
d^
```

**Paste** This operation is performed using `p` command to paste the selected text

```cmd
p
```

2. **Visual Mode** In this mode, first select the text using below keys

1. v (lowercase): To select individual characters
2. V (uppercase): To select the entire line
3. Ctrl+v: To select by block

and perform copy, cut and paste operations using y,d and p commands

##### 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
```

**[⬆ Back to Top](#table-of-contents)**

### Top/TaskManager Command

top: The `top` command provides dynamic real-time viewing of the running system. It can display system summary information as well as a list of tasks currently being managed by the Linux kernel.

#### options
| Option | Description |
|--------|------------------------------------------|
| -b | Batch mode |
| -n | Number of iterations |
| -s | Sec delay between updates |
| -d | Delay time in seconds |
| -p | Monitor process ID |

```cmd
top [options]
```

**[⬆ Back to Top](#table-of-contents)**

### Kill Command
kill: The kill command sends a signal to a process. Useful when trying to terminate a hung process.

**options:**
| Option | Description |
|--------|-----------------------------------------------|
| -s | Specify the signal to send (e.g., -s SIGTERM) |
| -l | List available signals |
| -n | Process group ID |
| -signal| Specify the signal using signal name or number|
| -p | Specify the process ID to be signaled |

#### kill Command Options

1. -s Option
Specifies the signal to send to the process. Use in the format -s SIGNAL. For example:

```cmd
kill -s SIGTERM
```

2. -l Option
Lists available signals that can be used with the kill command. This option does not send any signal; it only displays a list of signals.

```cmd
kill -l
```
3. -n Option
Specifies the process group ID. This option allows you to send a signal to a process group rather than an individual process.

```cmd
kill -n
```
4. -signal Option
Specifies the signal to send using either the signal name or number directly.

```cmd
kill -TERM
```
5. -p Option
Specifies the process ID to be signaled. Use in the format -p .

```cmd
kill -p
```

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### History Command Options
The history command shows a list of previously issued commands.

#### history Command Options
| Option | Description |
|----------------|-------------------------------------------------------------|
| `-c` | Clears the entire command history. |
| `-d offset` | Deletes the history entry at the specified offset. |
| `-a` | Appends the current session's history to the history file. |
| `-r` | Reads the history file and appends entries to the session. |
| `-n` | Prevents command numbers from being displayed. |
| `-w` | Writes the current session's history to the history file. |
| `-s ""| Appends the specified entry to the end of the history list. |
| `-p offset` | Prints the history entry at the specified offset. |
| `-f file` | Reads history entries from the specified file. |

1. -c Option
Clears the entire command history.
```cmd
history -c
```

2. -d offset Option
Deletes the history entry at the specified offset.

```cmd
history -d
```

3. -a Option
Appends the current session's history to the history file.

```cmd
history -a
```

4. -r Option
Reads the history file and appends the entries to the current session's history.

```cmd
history -r
```

5. -n Option
Prevents command numbers from being displayed when using the history command.

```cmd
history -n
```
6. -w Option
Writes the current session's history to the history file.

```cmd
history -w
```

7. -s Option
Appends the specified entry to the end of the history list.

```cmd
history -s ""
```

8. -p Option
Prints the history entry at the specified offset.

```cmd
history -p
```

9. -f file Option
Reads history entries from the specified file and appends them to the history list.

```cmd
history -f
```

**[⬆ Back to Top](#table-of-contents)**

### Curl Command

Curl: The curl command transfers data to or from a server. It supports dozens of protocols, including HTTP, HTTPS, FTP, SFTP, Telnet, DICT, LDAP, LDAPS, FILE, IMAP, SMTP, POP3, RTSP and RTMP.

**Options**

| Option
|----------------
| `-X, --request `
| `-H, --header `
| `--data `
| `--data-urlencode `
| `--form `
| `-d, --data-raw `
| `-i, --include`
| `--url `
| `-o, --output `
| `-O, --remote-name`
| `-L, --location`
| `--user `
| `-u, --user-agent
| `--cookie `
| `--cookie-jar `
| `--compressed`
| `-v, --verbose`
| `-h, --help` | Description | ------------|---------------------------------------------------------| | Specify the HTTP request method (GET, POST, etc.). | | Pass custom headers to the request. | | HTTP POST data. | | URL encode the POST data. | | Specify multipart/form-data POST data. | | Send data as-is without any encoding. | | Include HTTP headers in the output. | | Specify the URL to send the request to. | | Write output to a file instead of stdout. | | Save the file with the same name as in the URL. | | Follow redirects. | | Specify the user and password for server authentication.| ` | Set the user-agent string. | | Send cookies from string/file. | | Save cookies to a file after receiving them. | | Request compressed response. | | Make the operation more talkative for debugging. | | Display help information. |

1. Basic GET Request:
Sends a simple GET request to the specified URL.

```cmd
curl http://example.com
```

2. Specify Request Method:
Specifies a request method other than the default GET.

```cmd
curl -X POST http://example.com
```
3. Include Headers:

Includes custom headers in the request.

```cmd
curl -H "Content-Type: application/json" http://example.com
```
4. Send POST Data:
Sends data as POST request payload.

```cmd
curl -X POST --data "key1=value1&key2=value2" http://example.com
```

5. Save Output to File:
Writes the output to a specified file.

```cmd
curl -o output.html http://example.com
```
6. Download File:
Downloads a file and saves it with the same name as in the URL.

```cmd
curl -O http://example.com/file.zip
```

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