chmod 500 (r-x------)

chmod 500 (r-x------) gives the owner read and execute, the group no permissions, and everyone else no permissions.

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Symbolic rwxr-xr-x
Read (4)Write (2)Execute (1)
Owner
Group
Others
Special
chmod 755 file

What chmod 500 means

ClassDigitPermissions
Owner5read and execute
Group0no permissions
Others0no permissions

Check that each class has only the access it needs (principle of least privilege).

chmod 500 file.txt          # one file
find /var/www -type f -exec chmod 500 {} +   # all files in a tree

How octal permissions work

Each digit is the sum of read (4), write (2) and execute (1) for owner, group and others. So 7 = 4+2+1 = rwx, 5 = 4+1 = r-x, 4 = r--. An optional leading digit sets special bits: setuid (4), setgid (2) and sticky (1) โ€” e.g. 1777 is /tmp.

Safe defaults for web servers

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