chmod 644 (rw-r--r--)

chmod 644 (rw-r--r--) gives the owner read and write, the group read, and everyone else read.

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

What chmod 644 means

ClassDigitPermissions
Owner6read and write
Group4read
Others4read

The standard for regular files such as web content and config: everyone can read, only the owner can write.

chmod 644 file.txt          # one file
find /var/www -type f -exec chmod 644 {} +   # 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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