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51f3df Niklas Polke 2026-08-05 22:24:08
Create CHMOD
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# CHMOD
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The chmod command is used to change file and directory permissions in Linux and Unix-based systems. Permissions can be specified using either numeric (octal) or symbolic (letter) notation.
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## Numeric (Octal) Notation
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Each permission is represented by a number:
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```
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4 = Read (r)
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2 = Write (w)
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1 = Execute (x)
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```
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The values are added together for each user category:
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```
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Owner
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Group
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Others
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```
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Example: `chmod 755 script.sh`
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This results in:
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```
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Owner: rwx (7 = 4+2+1)
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Group: r-x (5 = 4+1)
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Others: r-x (5 = 4+1)
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```
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## Symbolic (Letter) Notation
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Permissions can also be modified using letters:
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```
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u = User (owner)
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g = Group
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o = Others
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a = All users
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```
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Operators:
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```
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+ = Add permission
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- = Remove permission
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= = Set exact permission
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```
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Examples:
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```
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chmod u+x script.sh # Add execute permission for the owner
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chmod g-w file.txt # Remove write permission from the group
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chmod a=r file.txt # Set read-only permission for everyone
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```
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Both notations achieve the same result. Numeric notation is commonly used for setting complete permission sets, while symbolic notation is useful for modifying specific permissions.
213eda Niklas Polke 2026-08-05 22:57:04
Update Special Bits
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## Special Bits
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| Bit | Octal | Letter | on file | on directory |
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| - | - | - | - | - |
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| Setuid | 4 | u+s | program runs with uid of file | --- |
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| Setgid | 2 | g+s | program runs with gid of file | directory passes group of directory to new files/directories beneath |
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| Sticky | 1 | +t | --- | the files within the directory are only deletable and renamable from owner of directory or file |
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example:
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```
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3770 Setgid + Sticky-Bit + rwx for user, rwx for group and none for other
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```