crealf - Linux

Overview

crealf (Create Real File) converts a virtual file in a Linux cgroup to a real file on disk. This allows access to files in cgroups from outside the container.

Syntax

crealf [-f] [-d DIR] [-m MODE] [-g ID] [-u ID] FILE

Options/Flags

  • -f: Force overwrite of existing file.
  • -d DIR: Path to store the file. Defaults to the current working directory.
  • -m MODE: File permissions (in octal). Defaults to 0644.
  • -g ID: Group ID of the file. Defaults to the user’s current primary group.
  • -u ID: User ID of the file. Defaults to the user’s current effective user ID.
  • FILE: The virtual file to convert.

Examples

Convert a virtual file to a real file:

crealf /sys/fs/cgroup/memory/foo/memory.limit_in_bytes

Convert a virtual file to a real file in a specific directory:

crealf -d /tmp /sys/fs/cgroup/memory/foo/memory.limit_in_bytes

Common Issues

  • Permission denied error: Ensure that you have root privileges or sufficient permissions to access the cgroup and the destination file.
  • File not found error: Double-check the path to the virtual file and make sure that the cgroup is mounted.

Integration

crealf can be integrated with other commands to perform advanced tasks:

  • Mount cgroups: Use mount -t cgroup cgroup MOUNTPOINT to mount cgroups before accessing virtual files.
  • Chain commands: Use pipes to chain crealf with other commands, e.g., crealf FILE | grep PATTERN.

Related Commands

  • cgroups: Manage control groups.
  • mount: Mount filesystems and cgroups.
  • chown: Change file ownership.