What do the numeric values used in setting access rights with the chmod command mean?

Numerical values in the chmod command specify access rights to files and directories in Unix-like systems. Each number is a sum of permissions for three user categories: owner, group, and others.

Each permission is encoded as a number:

• 4 — read (r)
• 2 — write (w)
• 1 — execute (x)

For example, 7 (4+2+1) means full access (read, write, execute), 6 (4+2) means read and write, 5 (4+1) means read and execute.

The command chmod 754 file sets:

• owner: 7 (rwx)
• group: 5 (r-x)
• others: 4 (r--)

Thus, the three digits define permissions for owner, group, and others in sequence.