bash Cookbook

Clearing the Command Hash

Problem

You need to make sure that your command hash has not been subverted.

Solution

Use the hash -r command to clear entries from the command hash.

Discussion

On execution, bash “remembers” the location of most commands found in the $PATH to speed up subsequent invocations.

If an attacker can trick root or even another user into running a command, they will be able to gain access to data or privileges they shouldn’t have. One way to trick another user into running a malicious program is to poison the hash so that the wrong program may be run.

See Also

• Finding World-Writable Directories in Your $PATH

• Adding the Current Directory to the $PATH

• Setting a POSIX $PATH

• Change Your $PATH Permanently

• Change Your $PATH Temporarily

• Forgetting That the Current Directory Is Not in the $PATH