/proc/mounts

The /proc/mounts file in Linux provides information about all the mounted filesystems. It is a part of the /proc filesystem, which is a virtual filesystem that presents information about the system's processes and other kernel-related information.

Structure and Contents

The contents of /proc/mounts are presented in a tabular format, with each line representing a mounted filesystem. The typical columns found in /proc/mounts are as follows:

1. Device: The device or special file associated with the filesystem.

2. Mount Point: The directory where the filesystem is mounted.

3. Filesystem Type: The type of filesystem (e.g., ext4, nfs, tmpfs).

4. Mount Options: Options used to mount the filesystem.

5. Dump: Used by the dump command to determine which filesystems need to be dumped.

6. Pass: Used by the fsck command to determine the order in which filesystems should be checked at boot time.

Example Output

Here is an example of what the /proc/mounts file might look like:

/dev/sda1 / ext4 rw,relatime,errors=remount-ro 0 1
/dev/sda2 /home ext4 rw,relatime 0 2
tmpfs /run tmpfs rw,nosuid,nodev,noexec,relatime,size=8156160k,mode=755 0 0
tmpfs /dev/shm tmpfs rw,nosuid,nodev 0 0

Columns Explained

• Device: This could be a physical device (like /dev/sda1), a virtual device (like tmpfs), or a network file system (like nfs).

• Mount Point: The directory where the filesystem is accessible. The root filesystem is typically mounted at /, while other filesystems may be mounted at directories like /home or /run.

• Filesystem Type: Indicates the type of filesystem, such as ext4 for the ext4 filesystem, tmpfs for temporary filesystems, and nfs for Network File System.

• Mount Options: Options used during the mounting process. Common options include rw (read-write), ro (read-only), relatime (update inode access times relative to modify/change times), nosuid (disallow set-user-identifier or set-group-identifier bits), and others.

• Dump: A numeric value indicating whether the filesystem should be dumped (1 for yes, 0 for no).

• Pass: A numeric value indicating the order in which fsck should check filesystems at boot time. The root filesystem is usually checked first (pass 1), and other filesystems are checked afterwards (pass 2).

Practical Uses

Checking Mounted Filesystems

To quickly see which filesystems are currently mounted, you can simply view the contents of /proc/mounts:

cat /proc/mounts

Using /proc/mounts in Scripts

Since /proc/mounts provides a reliable and up-to-date list of mounted filesystems, it is often used in scripts to check for specific mounts or to gather information about the filesystem state.

For example, to check if /home is mounted:

grep " /home " /proc/mounts

Monitoring Filesystem Mounts

System administrators can monitor /proc/mounts to detect changes in the mounted filesystems. This can be useful for debugging issues related to mounts or to ensure that critical filesystems are always mounted.

Difference Between /proc/mounts and /etc/mtab

• /proc/mounts: This file is maintained by the kernel and always contains an up-to-date list of all mounted filesystems.

• /etc/mtab: This file is maintained by the mount command and other utilities. It may not always be up-to-date or accurate if mounts are performed by methods other than mount.

Conclusion

The /proc/mounts file is a valuable resource for system administrators and scripts that need to obtain real-time information about the mounted filesystems. Understanding its structure and content allows for effective monitoring and management of filesystem mounts on a Linux system.