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