chmod 2775 rwxrwsr-x

chmod 2775 (rwxrwsr-x): the owner can read, write and execute, the group read, write and execute, others read and execute, with setgid. Commands and umask.

Octal: 2775
Symbolic: rwxrwsr-x
ls -l shows: -rwxrwsr-x for a file, drwxrwsr-x for a directory
chmod letters: u=rwx,g=rwxs,o=rx

Who can do what

Class	Digit	Bits	On a file	On a directory
Owner (u)	7	`rwx`	Read the contents, change or empty the contents and run it as a program	List the names inside, create, delete and rename entries and enter it and open files by name
Group (g)	7	`rwx`	Read the contents, change or empty the contents and run it as a program	List the names inside, create, delete and rename entries and enter it and open files by name
Others (o)	5	`r-x`	Read the contents and run it as a program	List the names inside and enter it and open files by name

Each digit adds read (4), write (2) and execute (1). Deleting or renaming a file depends on write and execute on the directory that holds it, not on the file's own mode. Root bypasses read and write checks.

Special bits

Setgid (2): On a program: it runs with the file's group. On a directory: new files and subdirectories take the directory's group, and new subdirectories inherit setgid. Shown as s in the group's execute place.

Typical uses

Setgid plus 775: the classic shared team directory. Group members can create files, and every new file and subdirectory belongs to the directory's group, so the team keeps access. Pair it with umask 002 so new files are group-writable.

Security notes

The group can write, so check who is in the group; adding a user to it gives them write access.
Setgid on a program lets anyone run it with the file's group; on a directory it only changes group ownership of new files, which is harmless.
Every account on the machine can read it, so keep passwords, keys and tokens out of anything with this mode.

Commands

Numeric
chmod 2775 file
Symbolic
chmod u=rwx,g=rwxs,o=rx file
Check the result
stat -c '%a %A %n' file
Directories only, recursively
find /path -type d -exec chmod 2775 {} +

Avoid chmod -R 2775 on a tree that holds files as well as folders: it makes every file executable. Use the find command above for directories and a file mode such as 644 for the files.

The umask that gives 2775

No umask produces 2775: a umask only removes bits from 666 for files and 777 for directories, and it never sets setuid, setgid or the sticky bit. Set it with chmod after creating the file or directory.

Other common modes

Work out any other mode in the chmod calculator