A script must be readable and executable by everyone but writable only by its owner. Which octal mode does that?
LPIC-1 Exam 101-500, objective 104. Devices, Linux filesystems, filesystem hierarchy standard easy
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The options
Not correct 644
Wrong for a script. 644 is rw-r--r--: nobody may execute it, so running it directly fails with 'Permission denied'. This is the right mode for a data or configuration file.
Correct 755
Correct. Owner 7 = rwx, group 5 = r-x, other 5 = r-x. Exactly read plus execute for everyone, write for the owner only.
Not correct 777
Wrong, and a security problem. rwxrwxrwx lets any user on the system rewrite the script, and whoever later runs it executes their code.
Not correct 750
Wrong here only because of 'everyone'. rwxr-x--- gives the owner and group members read and execute but denies all access to others. It is the correct choice when the script should stay inside one group.
Why
Each octal digit is the sum of read 4, write 2, execute 1, applied to owner, group and other in that order. 755 rwxr-xr-x, 750 rwxr-x---, 644 rw-r--r--, 700 rwx------. The same change symbolically would be `chmod u=rwx,go=rx file`.
Where this comes from
- Cited
- LPI exam objective 104.5
- What it says
- Manage access permissions using both symbolic and octal modes of chmod.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 104 and space the ones you get wrong.