Fix "Permission denied" Errors in Linux

How Linux permissions work

Every file and folder has three kinds of permission:

1. Read (r)
2. Write (w)
3. Execute (x)

They apply to three groups: the owner, the group and others. See them with:

ls -la

For example -rwxr-xr-- means: the owner can read, write and run; the group can read and run; others can only read.

Why you get "Permission denied"

• The file or folder belongs to another user or group.
• The permissions are wrong.
• You try to reach a system file without root rights.
• The script is not set as executable.

Fixes

1. Change the permissions. If you have the right to, add what is missing. Give the owner read, write and execute:

chmod u+rwx test.sh

2. Take ownership. If you are root or have sudo, give the file to your user:

sudo chown username test.sh

3. Use sudo. If you are not the owner and a system folder is involved, run the command as root:

sudo mkdir /opt/test

Use sudo only when you need it.

Permission denied when running a script

Make the script executable and run it:

chmod +x test.sh
./test.sh

If you still get an error, the file system may be mounted with noexec. Run the script with bash test.sh instead.

Other causes

• A parent folder has no execute (x) permission. You need x on every folder in the path.
• SELinux or AppArmor blocks the access. Check the logs (/var/log/audit/audit.log).
• SSH keys: the private key must have mode 600 (chmod 600 ~/.ssh/id_rsa).

Quick recap

• Read the permissions with ls -la.
• Use chmod, chown or sudo to fix the access.
• Make scripts executable with chmod +x.