chmod 640 Permission Explained: Owner Edit, Group Read

Octal

640

Symbolic

rw-r-----

Binary

110 100 000

Risk Level

Low Risk

Summary: Group can read; others have no access.

Class	Read (4)	Write (2)	Execute (1)	Octal
Owner (u)				6
Group (g)				4
Others (o)				0

setuid (4) setgid (2) sticky bit (1)

Octal

Symbolic

Target File / Path

-R Recursive -v Verbose

640

rw-r-----

Owner: read/write · Group: read · Others: no access

chmod 640 filename

Low Risk

View the full chmod 640 guide →

chmod 640 Breakdown

Class	Digit	Symbolic	On a file	On a directory
Owner (u)	`6`	`rw-`	Read and write	Can list names, cannot enter
Group (g)	`4`	`r--`	Read only	Can list names, but not enter
Others (o)	`0`	`---`	No access	Cannot list, enter, or modify

Is chmod 640 Safe?

Low Risk

This permission configuration follows standard Linux access control principles with no elevated risk indicators.

When not to use it

Public web assets that must be served directly to all local processes

Common Use Cases

Server configuration files containing sensitive database passwords read by daemons
Application logs read by auditing or monitoring groups

chmod 640 Command Examples

# Apply using octal mode
chmod 640 filename

# Apply using equivalent symbolic mode
chmod u=rw,g=r,o= filename

# Recursive command warning:
chmod -R 640 /path/to/dir
# Note: -R applies the same mode to files and directories. Use find to treat them separately:
find /path/to/dir -type f -exec chmod 640 {} +

# Verify permissions
stat -c '%a %A %n' filename    # Linux
stat -f '%Lp %Sp %N' filename   # macOS

# Example ls -l output:
-rw-r----- 1 alice staff 1024 Jan 15 10:00 example.txt

umask Relationship

A umask of 137 makes new directories 640 and new files 640. Test umask values with our interactive Umask Calculator.

Frequently Asked Questions

What does chmod 640 mean?

Group can read; others have no access. In octal notation, the owner receives 6 (read/write), the group receives 4 (read), and others receive 0 (no access).

Is chmod 640 safe?

chmod 640 is classified as Low Risk. It follows standard Linux access patterns.

What is chmod 640 in symbolic notation?

In symbolic notation, chmod 640 is represented as rw-r-----. You can apply this permission using the equivalent symbolic command "chmod u=rw,g=r,o= filename".

Related Permissions

Change one bit:

chmod 240 remove owner read chmod 440 remove owner write chmod 740 add owner execute chmod 600 remove group read chmod 660 add group write chmod 650 add group execute chmod 644 add others read chmod 642 add others write chmod 641 add others execute

← chmod 637 chmod 641 →

Related Guides

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