cap_set_flag - Linux

Overview

cap_set_flag is a powerful tool used to manipulate file capabilities in the Linux operating system. By setting or clearing specific capability flags, you can grant or revoke special privileges to processes or files, enhancing their security or functionality.

Syntax

cap_set_flag [options] ACTION CAPABILITY [FILE...]

Parameters

  • ACTION (set or clear): Indicates whether to set or clear the specified capability.
  • CAPABILITY: The name of the capability to modify (e.g., CAP_DAC_READ_SEARCH, CAP_SYS_CHROOT).
  • FILE…: The file or files to modify the capabilities for. If not specified, the current process is affected.

Options/Flags

  • -e: Print a message if the specified file does not exist.
  • -v: Be verbose and print more information about the operation.
  • -P: Change capability property (only for files, see Common Issues).
  • -f: Force the operation even if it would result in an error.

Examples

Setting a Capability

To grant the CAP_SYS_CHROOT capability to the file /tmp/test.file:

cap_set_flag set CAP_SYS_CHROOT /tmp/test.file

Clearing a Capability

To revoke the CAP_DAC_READ_SEARCH capability from the file /etc/passwd:

cap_set_flag clear CAP_DAC_READ_SEARCH /etc/passwd

Common Issues

  • File Not Found: If the specified file does not exist and the -e option is not used, the command may silently fail.
  • Capability Property: For files, use the -P option to modify the file’s capability property rather than the process’s capabilities.
  • CAP_SYS_ADMIN: Modifying the CAP_SYS_ADMIN capability requires root privileges.

Integration

cap_set_flag can be integrated with other Linux commands to enhance security or automate tasks.

  • With find: Search for files with specific capabilities and apply changes:
find . -type f -exec cap_set_flag set CAP_DAC_OVERRIDE {} \;
  • With sudo: Grant or revoke capabilities to processes run by specific users:
sudo cap_set_flag set CAP_SYS_CHROOT $USER /tmp/test

Related Commands

  • getcap: Retrieve the capabilities of a process or file.
  • chattr: Change file attributes, including capabilities.
  • capabilities(7): Linux man page on capabilities.