--- obj: concept rev: 2024-07-08 --- # Mount Mounting is a fundamental concept in Linux and other Unix-like operating systems, enabling users to access and manage filesystems, storage devices, and partitions. Mounting is the process of making a filesystem accessible at a certain point in the directory tree. When you mount a storage device or a partition, you attach it to a specified directory, known as a mount point. This allows you to access the contents of the device or partition as if they were part of the overall filesystem. ## `mount` Command Usage: ```shell mount [options] [source] [mount_point] # Bind Mounts mount --bind /var/www /mnt/www # Loop Device mount -o loop /path/to/file.iso /mnt/iso # List mounts mount -l ``` The source of the filesystem can be specified in other ways too (depending on the filesystem): - `LABEL=label`: Human readable filesystem identifier. - `UUID=uuid`: Filesystem universally unique identifier. The format of the UUID is usually a series of hex digits separated by hyphens. - `PARTLABEL=label`: Human readable partition identifier. This identifier is independent on filesystem and does not change by mkfs or mkswap operations. It’s supported for example for GUID Partition Tables (GPT). - `PARTUUID=uuid`: Partition universally unique identifier. This identifier is independent on filesystem and does not change by mkfs or mkswap operations. It’s supported for example for GUID Partition Tables (GPT). ### Options | Option | Description | | -------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `-a, --all` | Mount all filesystems in `/etc/fstab`. | | `-B, --bind` | Mount a directory somewhere else | | `-m, --mkdir[=mode]` | Allow to make a target directory (mountpoint) if it does not exist yet. The default mode is `0755`. | | `-o, --options opts` | Use the specified mount options. The opts argument is a comma-separated list. | | `-r, --read-only` | Mount the filesystem read-only. A synonym is `-o ro`. | | `--source device` | This option allows you to explicitly define that the argument is the mount source. | | `--target directory` | This option allows you to explicitly define that the argument is the mount target. | | `-t, --types fstype` | The argument following `-t` is used to indicate the filesystem type. The filesystem types which are currently supported depend on the running kernel. See `/proc/filesystems` and `/lib/modules/$(uname -r)/kernel/fs` for a complete list of the filesystems. | ## `/etc/fstab` The `/etc/fstab` file is used to define filesystems to be automatically mounted at boot time. Nowadays the entries in this file will be converted to [Systemd-Mounts](systemd/Systemd-Mounts.md). Each file contains a mount instruction like this: `DEVICE MOUNT_POINT FILESYSTEM_TYPE OPTIONS DUMP PASS` Example: `/dev/sdb1 /mnt/usb ext4 defaults 0 2` - `DEVICE`: The device or partition to be mounted. - `MOUNT_POINT`: The directory where the filesystem will be mounted. - `FILESYSTEM_TYPE`: The type of filesystem. - `OPTIONS`: Mount options (e.g., `defaults`, `ro`, `rw`). - `DUMP`: Used by the `dump` utility to decide if a filesystem should be backed up. - `PASS`: Used by `fsck` to determine the order in which filesystems are checked. ## Mount Options - `async`: All I/O to the filesystem should be done asynchronously. - `atime`: Update inode access times on each access. - `noatime`: Do not update inode access times on each access (useful for performance). - `auto`: Can be mounted with the `mount -a` command. - `noauto`: Can only be mounted explicitly. - `defaults`: Use default options (`rw`, `suid`, `dev`, `exec`, `auto`, `nouser`, and `async`). - `dev`: Interpret character or block special devices on the filesystem. - `nodev`: Do not interpret character or block special devices on the filesystem. - `diratime`: Update directory inode access times on each access. - `nodiratime`: Do not update directory inode access times on each access. - `dirsync`: All directory updates within the filesystem should be done synchronously. - `exec`: Permit execution of binaries. - `noexec`: Do not permit execution of any binaries. - `group`: Allow an ordinary user to mount the filesystem if they are a member of the group owning the device. - `iversion`: Increment the inode version field upon each change. - `mand`: Allow mandatory locks on this filesystem. - `nomand`: Do not allow mandatory locks on this filesystem. - `relatime`: Update inode access times relative to modify or change time. - `norelatime`: Do not use the `relatime` feature. - `lazytime`: Only update times on the in-memory version of an inode. - `nolazytime`: Do not use the `lazytime` feature. - `ro`: Mount the filesystem read-only. - `rw`: Mount the filesystem read-write. - `suid`: Permit set-user-identifier or set-group-identifier bits to take effect. - `nosuid`: Do not permit set-user-identifier or set-group-identifier bits to take effect. - `silent`: Suppress some error messages. - `loud`: Do not suppress error messages. - `strictatime`: Strictly update inode access times on each access. ### Filesystem-Specific Options Each filesystem type may support its own set of mount options. Here are some examples for a few common filesystems: #### ext2, ext3, ext4 - `acl`: Enable POSIX Access Control Lists. - `noacl`: Disable POSIX Access Control Lists. - `user_xattr`: Enable user extended attributes. - `nouser_xattr`: Disable user extended attributes. - `journal`: Enable journaling (ext3/ext4). - `nojournal`: Disable journaling (ext3/ext4). #### btrfs - `compress`: Enable compression. - `compress-force`: Force compression. - `nodatacow`: Disable copy-on-write for data blocks. - `nodatasum`: Disable data checksumming. - `subvol`: Mount a specific subvolume. #### xfs - `logbufs`: Number of in-memory log buffers. - `logbsize`: Size of each in-memory log buffer. - `noquota`: Disable quota enforcement. - `quota`: Enable quota enforcement. #### nfs - `rsize`: Set the read buffer size. - `wsize`: Set the write buffer size. - `timeo`: Set the timeout value. - `intr`: Allow interrupts on hard mounts. - `nointr`: Do not allow interrupts on hard mounts. #### vfat - `shortname`: Define behavior for handling of short filenames. - `iocharset`: Character set to use for input and output. - `utf8`: Encode and decode 8-bit characters as UTF-8. ### Network Filesystems #### cifs (Common Internet File System) - `username`: Username to connect to the CIFS share. - `password`: Password to connect to the CIFS share. - `domain`: Domain name for authentication. - `uid`: Set the owner of the files. - `gid`: Set the group of the files. #### nfs (Network File System) - `vers`: Specify NFS version. - `proto`: Specify transport protocol (`tcp` or `udp`). - `mountport`: Specify port number for MOUNT service.