Unexpected Causes of “Permission denied” in Linux and How to Fix Them

When using Linux, you may occasionally encounter the “Permission denied” error. While this usually indicates insufficient access rights to a file or directory, there are several unexpected reasons why it can occur.

In this article, we’ll explain some surprising causes and how to resolve them.

目次

1. Understanding Basic Permissions

In Linux, every file and directory has associated permissions. These permissions define read (r), write (w), and execute (x) access for:

  • The file owner
  • The group
  • Other users

You can view permissions with:

$ ls -l
-rwxr-xr-- 1 user group 1234 Jan 1 12:00 example.sh

Explanation of the output:

  • -rwxr-xr--: file permissions
    • rwx: owner permissions (read, write, execute)
    • r-x: group permissions (read, execute)
    • r--: others’ permissions (read only)
  • user: file owner
  • group: file group
  • 1234: file size
  • Jan 1 12:00: last modified date
  • example.sh: file name

2. Unexpected Reason: Missing Execute Permission on Directories

To access a file, you also need execute permission on the directory containing the file. For example:

$ ls -l /home/user
drwxr-xr-- 2 user group 4096 Jan 1 12:00 mydir

Here, the directory mydir lacks execute permission for the group and others, preventing them from accessing files inside it.

Solution:

Add execute permission for the group:

$ chmod g+x /home/user/mydir

3. Unexpected Reason: SELinux Restrictions

SELinux (Security-Enhanced Linux) can enforce additional access control. Even if standard file permissions are correct, SELinux policies may block access.

Solution:

Check SELinux status:

$ sestatus

If SELinux is enforcing restrictions, you can restore the correct context:

$ restorecon -R /path/to/directory

4. Unexpected Reason: Filesystem Mount Options

Certain mount options can restrict access. For example, a filesystem mounted with the noexec option prevents execution of files, even if they have execute permission.

Solution:

Check mount options:

$ mount | grep /path/to/mount

If noexec is set, remount with exec:

$ sudo mount -o remount,exec /path/to/mount

You may also need to update /etc/fstab for permanent changes.

5. Unexpected Reason: File Ownership

If a file is owned by another user, other users may not have access:

$ ls -l /path/to/file
-rw-r----- 1 otheruser group 1234 Jan 1 12:00 secret.txt

Only otheruser can read this file.

Solution:

Change the file owner:

$ sudo chown yourusername /path/to/file

6. Unexpected Reason: Incorrect Shebang in Scripts

If a script’s shebang (the first line) is incorrect, running it may result in a “Permission denied” error.

Example:

#!/bin/bash
echo "Hello, World!"

If the shebang is wrong, the script won’t execute.

Solution:

Ensure the correct shebang and make the script executable:

$ chmod +x /path/to/script.sh

7. Unexpected Reason: Insufficient Disk Space

If the disk is full, new files cannot be created or written, leading to “Permission denied” errors. This is especially common when the root partition is full.

Solution:

Check disk space:

$ df -h

If space is low, delete unnecessary files or move data to another partition.

8. Summary

The causes of “Permission denied” errors in Linux are varied:

  • File and directory permissions
  • SELinux policies
  • Filesystem mount options
  • File ownership
  • Incorrect shebang lines in scripts
  • Low disk space

Understanding these factors and addressing them appropriately will help you resolve the error and continue working smoothly.

References

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