chmod 040 Permission Explained
Summary: chmod 040 gives the owner no access, the group read, and everyone else no access.
| Class | Read (4) | Write (2) | Execute (1) | Octal |
|---|---|---|---|---|
| Owner (u) | 0 | |||
| Group (g) | 4 | |||
| Others (o) | 0 |
chmod 040 filename
chmod 040 Breakdown
| Class | Digit | Symbolic | On a file | On a directory |
|---|---|---|---|---|
| Owner (u) | 0 |
--- |
No access | Cannot list, enter, or modify |
| Group (g) | 4 |
r-- |
Read only | Can list names, but not enter |
| Others (o) | 0 |
--- |
No access | Cannot list, enter, or modify |
Is chmod 040 Safe?
Low Risk
- 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
040 is uncommon in standard Linux setups. The closest widely used permission is chmod 440.
chmod 040 Command Examples
# Apply using octal mode
chmod 040 filename
# Apply using equivalent symbolic mode
chmod u=,g=r,o= filename
# Recursive command warning:
chmod -R 040 /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 040 {} +
# Verify permissions
stat -c '%a %A %n' filename # Linux
stat -f '%Lp %Sp %N' filename # macOS
# Example ls -l output:
----r----- 1 alice staff 1024 Jan 15 10:00 example.txtumask Relationship
A umask of 737 makes new directories 040 and new files 040. Test umask values with our interactive Umask Calculator.
Frequently Asked Questions
What does chmod 040 mean?
chmod 040 gives the owner no access, the group read, and everyone else no access. In octal notation, the owner receives 0 (no access), the group receives 4 (read), and others receive 0 (no access).
Is chmod 040 safe?
chmod 040 is classified as Low Risk. Even the owner cannot modify this file without changing permissions first.
What is chmod 040 in symbolic notation?
In symbolic notation, chmod 040 is represented as ---r-----. You can apply this permission using the equivalent symbolic command "chmod u=,g=r,o= filename".
Related Permissions
Change one bit: