/etc/mtab

1. Purpose:

   • /etc/mtab (mounted table) is a file used to record currently mounted filesystems and their options on a Linux system.

   • It dynamically reflects the current state of mounted filesystems and is updated automatically whenever a filesystem is mounted or unmounted.

2. Format:

   • Each line in /etc/mtab contains information about a mounted filesystem:

     /dev/sda1 / ext4 rw,relatime 0 0

     • Column 1: Device or filesystem path.

     • Column 2: Mount point in the directory tree.

     • Column 3: Filesystem type (e.g., ext4, nfs).

     • Column 4: Mount options (e.g., rw, relatime).

     • Column 5: Dump frequency (used by dump backup utility).

     • Column 6: Filesystem check order (used by fsck utility).

3. Usage:

   • Provides a real-time snapshot of currently mounted filesystems.

   • Used by system utilities and commands like mount, df, and umount to determine the current state of mounted filesystems.

4. Differences with /etc/fstab:

   • /etc/fstab: Static file used to define filesystems and their mount options for automatic mounting at system startup.

   • /etc/mtab: Dynamic file updated in real-time to reflect currently mounted filesystems.

5. Maintenance:

   • Normally managed automatically by the system.

   • Editing /etc/mtab directly is not recommended; changes may not persist across reboots.

6. Access:

   • Read access is typically required by system utilities to determine filesystem usage and status.

Conclusion

Understanding /etc/mtab provides insights into the current status of mounted filesystems on a Linux system. It serves as a vital reference for system administrators and utilities to manage and monitor filesystem usage dynamically. Always ensure to consult system documentation and use appropriate commands (mount, umount, df) to interact with mounted filesystems rather than editing /etc/mtab directly.