chmod 420 Permission Explained

Notice: This is an unusual permission set: some classes have more access than the class above them. It is rarely correct in practice.

Octal

420

Symbolic

r---w----

Binary

100 010 000

Risk Level

Moderate

Summary: chmod 420 gives the owner read, the group write, and everyone else no access.

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

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

Octal

Symbolic

Target File / Path

-R Recursive -v Verbose

420

r---w----

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

chmod 420 filename

Moderate Every member of the group can modify this file.

View the full chmod 420 guide →

chmod 420 Breakdown

Class	Digit	Symbolic	On a file	On a directory
Owner (u)	`4`	`r--`	Read only	Can list names, but not enter
Group (g)	`2`	`-w-`	Write only (rarely useful)	No practical effect without x
Others (o)	`0`	`---`	No access	Cannot list, enter, or modify

Is chmod 420 Safe?

Moderate

Every member of the group can modify this file.
Even the owner cannot modify this file without changing permissions first.
Unusual: a lower class has permissions the class above it lacks.

Common Use Cases

420 is uncommon in standard Linux setups. The closest widely used permission is chmod 400.

chmod 420 Command Examples

# Apply using octal mode
chmod 420 filename

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

# Recursive command warning:
chmod -R 420 /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 420 {} +

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

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

umask Relationship

A umask of 357 makes new directories 420 and new files 420. Test umask values with our interactive Umask Calculator.

Frequently Asked Questions

What does chmod 420 mean?

chmod 420 gives the owner read, the group write, and everyone else no access. In octal notation, the owner receives 4 (read), the group receives 2 (write), and others receive 0 (no access).

Is chmod 420 safe?

chmod 420 is classified as Moderate. Every member of the group can modify this file.

What is chmod 420 in symbolic notation?

In symbolic notation, chmod 420 is represented as r---w----. You can apply this permission using the equivalent symbolic command "chmod u=r,g=w,o= filename".

Related Permissions

Change one bit:

chmod 020 remove owner read chmod 620 add owner write chmod 520 add owner execute chmod 460 add group read chmod 400 remove group write chmod 430 add group execute chmod 424 add others read chmod 422 add others write chmod 421 add others execute

← chmod 417 chmod 421 →

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