chmod 421 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

421

Symbolic

r---w---x

Binary

100 010 001

Risk Level

Moderate

Summary: chmod 421 gives the owner read, the group write, and everyone else execute.

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

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

Octal

Symbolic

Target File / Path

-R Recursive -v Verbose

421

r---w---x

Owner: read · Group: write · Others: execute

chmod 421 filename

Moderate Every member of the group can modify this file.

View the full chmod 421 guide →

chmod 421 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)	`1`	`--x`	Execute only	Can enter (cd) but not list contents

Is chmod 421 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

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

chmod 421 Command Examples

# Apply using octal mode
chmod 421 filename

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

# Recursive command warning:
chmod -R 421 /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 421 {} +

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

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

umask Relationship

A umask of 356 makes new directories 421. Test umask values with our interactive Umask Calculator.

Frequently Asked Questions

What does chmod 421 mean?

chmod 421 gives the owner read, the group write, and everyone else execute. In octal notation, the owner receives 4 (read), the group receives 2 (write), and others receive 1 (execute).

Is chmod 421 safe?

chmod 421 is classified as Moderate. Every member of the group can modify this file.

What is chmod 421 in symbolic notation?

In symbolic notation, chmod 421 is represented as r---w---x. You can apply this permission using the equivalent symbolic command "chmod u=r,g=w,o=x filename".

Related Permissions

Change one bit:

chmod 021 remove owner read chmod 621 add owner write chmod 521 add owner execute chmod 461 add group read chmod 401 remove group write chmod 431 add group execute chmod 425 add others read chmod 423 add others write chmod 420 remove others execute

← chmod 420 chmod 422 →

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