etcmtab

The /etc/mtab file records the currently mounted filesystems on Unix-like systems. It provides a dynamic view of the kernel's mount state and is used by mounting utilities and system processes to determine what is mounted, where, and with which options.

Location and format: Traditionally, /etc/mtab is a plain text file containing one line per mounted filesystem. Each line typically includes the device, the mount point, the filesystem type, the mount options, and two numeric fields (dump and pass) related to backup and filesystem checks. On many Linux systems, /etc/mtab is a symbolic link to /proc/mounts or /proc/self/mounts, which means the file is effectively a view of the kernel's mount table rather than a separate, independently maintained file.

Management and sources: When /etc/mtab exists as a real file, it is updated by mount and umount operations to reflect changes in the mounted state. If it is a symlink to /proc/mounts, the kernel provides the authoritative data, and the content seen via /etc/mtab mirrors that source. Tools that report mounted filesystems, such as findmnt and mount, may read from /proc/mounts, /etc/mtab, or both, depending on the system configuration and the presence of the symlink.

Usage notes: /etc/mtab serves as a convenient, human-readable reference for administrators and scripts, but it is not always the authoritative source of truth. For scripting and portable behavior, programs often prefer reading /proc/mounts or using higher-level interfaces provided by libraries such as libmount. See also /proc/mounts, /proc/self/mounts, /etc/fstab, libmount, and util-linux.