Chmod Numeric Permissions Notation UNIX / Linux Command

Can you provide more information about chmod command octal mode number notation?

The command chmod changes the file mode bits of each given file according to mode, which can be either a symbolic representation of changes to make, or an octal number representing the bit pattern for the new mode bits. chmod never changes the permissions of symbolic links; the chmod system call cannot change their permissions. This is not a problem since the permissions of symbolic links are never used. However, for each symbolic link listed on the command line, chmod changes the permissions of the pointed-to file. In contrast, chmod ignores symbolic links encountered during recursive directory traversals.

UNIX / Linux chmod command

A bit mask created by ORing together zero or more of the following:

First digit in the above mode number is used to set setuid, setgid, or sticky bit. Each remain digit set permission for the owner, group, and world as follows:

1. 4 = r (Read)
2. 2 = w (Write)
3. 1 = x (eXecute)

So you end up creating the triplets for your user by adding above digits. For e.g.

• To represent rwx triplet use 4+2+1=7
• To represent rw- triplet use 4+2+0=6
• To represent r-- triplet use 4+0+0=4
• To represent r-x triplet use 4+0+1=5

To only give full permission to user, use it as follows:
chmod 0700 file.txt

• 0 - Use set setuid, setgid, or sticky bit
• 7 - Full permission for owner (rwx = 4+2+1=7)
• 0 - Remove group permission (--- = 0+0+0=0)
• 0 - Remove world permission (--- = 0+0+0=0)

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