The "Permission Denied" error while trying to execute a script on CentOS 7, even after setting the file's executable permission using chmod +x, can be caused by several factors. This article provides a detailed overview of potential causes and their solutions to effectively address this issue.
Causes and Solutions
1. Incomplete or Incorrect Paths to the Script
Cause: If you're running the script from another directory and not using an absolute path, the shell might fail to "find" the script, resulting in a "Permission Denied" error.
Solution: Ensure you're using the full path to the file when executing it, such as /home/user/script.sh, or navigate to the directory where the script is located before running it.
2. Insufficient Read and Execute Permissions on the Script
Cause: Even though the execute bit (+x) has been set, the user or group under which you're executing the script may not have sufficient permissions to read it.
Solution: Use the ls -l script.sh command to view the file permissions. If the user or group lacks read (r) permissions, use chmod to add them, for example, chmod +rx script.sh.
3. SELinux Blocking Script Execution
Cause: On CentOS 7 systems, SeLinux (Security Enhanced Linux) might prevent script execution if the file lacks the correct security context.
Solution: Use the ls -Z script.sh command to check the security context of the file. Missing or incorrect contexts can be corrected using chcon or by setting the appropriate SeLinux policy.
4. Mounted Partition with noexec
Cause: If the partition containing the script is mounted with the noexec option, it won't be possible to execute any executable files from that partition.
Solution: Check the /etc/fstab file or use the mount command to determine if the partition is mounted with the noexec option. If so, you'll need to remount the partition without this option or move the script to a partition without noexec.
5. Corrupted File System or Media
Cause: In some cases, the error may be due to a corrupted file system or the media itself where the script resides.
Solution: Running file system check and repair tools like fsck may resolve the issue. Ensure you have backups before attempting any repairs.
The "Permission Denied" error can be frustrating, but in most cases, it can be resolved by checking and adjusting file permissions, security context, or system configurations. Thoroughly diagnosing the problem will help determine the correct course of action for resolution.
