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Systems & Data Center · Foundational

Octal Permission Notation

A numeric representation of Linux permissions where read=4, write=2 and execute=1 are summed per owner, group and others.

Definition

Each digit represents one class: 7 (rwx), 6 (rw-), 5 (r-x), 4 (r--), 0 (---). A leading fourth digit sets special bits: 4 for SUID, 2 for SGID and 1 for sticky.

Example

chmod 750 script.sh gives the owner rwx, group r-x and others nothing.

Exam tip

Be fluent converting both ways: 644 is rw-r--r-- and 755 is rwxr-xr-x.

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