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# Device file

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Related articles

- Persistent block device naming

This article or section needs expansion.

Reason: Explain loop devices. (Discuss in Talk:Device file)

From Wikipedia:

  In Unix-like operating systems, a device file or special file is an interface to a device driver that appears in a file system as if it were an ordinary file.

On Linux they are in the `/dev` directory, according to the Filesystem Hierarchy Standard.

On Arch Linux the device nodes are managed by udev.

## Block devices

A block device is a special file that provides buffered access to a hardware device. For a detailed description and comparison of virtual file system devices, see Wikipedia:Device file#Block devices.

### Block device names

The beginning of the device name specifies the kernel's used driver subsystem to operate the block device.

Warning: Kernel name descriptors for block devices are not persistent and can change each boot, they should not be used in configuration files.

#### SCSI

Storage devices, like hard disks, SSDs and flash drives, that support the SCSI command (SCSI, SAS, UASP), ATA (PATA, SATA) or USB mass storage connection are handled by the kernel's SCSI driver subsystem. They all share the same naming scheme.

The name of these devices starts with `sd`. It is then followed by a lower-case letter starting from `a` for the first discovered device (`sda`), `b` for the second discovered device (`sdb`), and so on.

Examples:

- `/dev/sda` - device `a`, the first discovered device.
- `/dev/sde` - device `e`, the fifth discovered device.

#### NVMe

The name of storage devices, like SSDs, that are attached via NVM Express (NVMe) starts with `nvme`. It is then followed by a number starting from `0` for the device controller, `nvme0` for the first discovered NVMe controller, `nvme1` for the second, and so on. Next is the letter "n" and a number starting from `1` expressing the namespace on a controller, i.e. `nvme0n1` for first discovered namespace on first discovered controller, `nvme0n2` for second discovered namespace on first discovered controller, and so on.

Note: The kernel's assigned namespace number is not guaranteed to match the NVMe namespace ID (NSID).

Examples:

- `/dev/nvme0n1` - device `1` on controller `0`, the first discovered device on the first discovered controller.
- `/dev/nvme2n5` - device `5` on controller `2`, the fifth discovered device on the third discovered controller.

#### MMC

This article or section needs expansion.

Reason: Mention `/dev/mmcblkXboot{0,1}`[1] and `/dev/mmcblkXrpmb`[2]. (Discuss in Talk:Partitioning#mmcblk0p{1,2,3,4}, mmcblk0boot{0,1}, mmcblk0rpmb)

SD cards, MMC cards and eMMC storage devices are handled by the kernel's `mmc` driver and name of those devices start with `mmcblk`. It is then followed by a number starting from `0` for the device, i.e. `mmcblk0` for first discovered device, `mmcblk1` for second discovered device and so on.

Note: If an SD/MMC card reader uses the USB interface, the block devices will be handled by the SCSI driver subsystem and follow its naming scheme.

Examples:

- `/dev/mmcblk0` - device `0`, the first discovered device.
- `/dev/mmcblk4` - device `4`, the fifth discovered device.

#### SCSI optical disc drive

The name of optical disc drives (ODDs), that are attached using one of the interfaces supported by the SCSI driver subsystem, start with `sr`. The name is then followed by a number starting from `0` for the device, ie. `sr0` for the first discovered device, `sr1` for the second discovered device, and so on.

Udev also provides `/dev/cdrom` that is a symbolic link to `/dev/sr0`. The name will always be `cdrom` regardless of the drive's supported disc types or the inserted media.

Examples:

- `/dev/sr0` - optical disc drive `0`, the first discovered optical disc drive.
- `/dev/sr4` - optical disc drive `4`, the fifth discovered optical disc drive.
- `/dev/cdrom` - a symbolic link to `/dev/sr0`.

#### virtio-blk

The name of drives attached to a virtio block device (virtio-blk) interface start with `vd`. It is then followed by a lower-case letter starting from `a` for the first discovered device (`vda`), `b` for the second discovered device (`vdb`), and so on.

Note: Do no confuse virtio-blk with virtio-scsi which emulates a SCSI controller and thus follows the SCSI naming convention.

Examples:

- `/dev/vda` - device `a`, the first discovered device.
- `/dev/vde` - device `e`, the fifth discovered device.

#### Partition

Partition device names are a combination of the drive's device name and the partition number assigned to them in the partition table, i.e. `/dev/drivepartition`. For drives whose device name ends with a number, the drive name and partition number is separated with the letter "p", i.e. `/dev/driveppartition`.

Examples:

- `/dev/sda1` - partition `1` on `/dev/sda`.
- `/dev/nvme2n5p3` - partition `3` on `/dev/nvme2n5`.
- `/dev/mmcblk3p4` - partition `4` on `/dev/mmcblk3`.
- `/dev/vda1` - partition `1` on `/dev/vda`.
- `/dev/loop0p2` - partition `2` on `/dev/loop0`.

### Utilities

#### lsblk

The util-linux package provides the lsblk(8) utility which lists block devices, for example:

    $ lsblk --fs

    NAME   FSTYPE   LABEL       UUID                                 MOUNTPOINT
    sda
    ├─sda1 vfat                 C4DA-2C4D                            /boot
    ├─sda2 swap                 5b1564b2-2e2c-452c-bcfa-d1f572ae99f2 [SWAP]
    └─sda3 ext4                 56adc99b-a61e-46af-aab7-a6d07e504652 /

In the example above, only one device is available (`sda`), and that device has three partitions (`sda1` to `sda3`), each with a different file system.

You can use the `-o`/`--output` option to enable a specific list of output columns:

    # lsblk --output NAME,PTTYPE,PARTLABEL,FSTYPE,FSVER,LABEL,FSSIZE,FSAVAIL,FSUSE%,MOUNTPOINTS

    NAME             PTTYPE PARTLABEL       FSTYPE      FSVER LABEL          FSSIZE FSAVAIL FSUSE% MOUNTPOINTS
    sda              gpt
    └─sda1           gpt    cryptdata1      crypto_LUKS 2
      └─data1                               btrfs             data1            7.3T    2.3T    68% /mnt/data
    sdb              gpt
    └─sdb1           gpt    cryptdata2      crypto_LUKS 2
      └─data2                               btrfs             data1
    sdc              gpt
    └─sdc1           gpt    cappdata        crypto_LUKS 2
      └─appdata                             ext4        1.0   appdata          3.6T    3.4T     0% /mnt/appdata
    sdd              gpt
    └─sdd1           gpt    cappdata_backup crypto_LUKS 2
      └─appdata_back                        ext4        1.0   appdata_backup
    nvme1n1          gpt
    ├─nvme1n1p1      gpt    BACKUP_EFI      vfat        FAT32 EFI                4G    3.9G     2% /boot
    ├─nvme1n1p2      gpt    backup_swap
    ├─nvme1n1p3      gpt    csys1           crypto_LUKS 2
    │ └─sys1                                btrfs             arch1
    └─nvme1n1p4      gpt    cext1           crypto_LUKS 2
      └─ext1                                btrfs             ext0fs
    nvme0n1          gpt
    ├─nvme0n1p1      gpt    EFI             vfat        FAT32 EFI
    ├─nvme0n1p2      gpt    cswap
    ├─nvme0n1p3      gpt    csys0           crypto_LUKS 2     sys0parent
    │ └─sys0                                btrfs             arch0             60G   56.2G     3% /
    └─nvme0n1p4      gpt    cext0           crypto_LUKS 2
      └─ext0                                btrfs             ext0fs         389.2G  388.1G     0% /home

The above is based on the options provided by the `-f`/`--fs` argument with removal of UUID and addition of partition label and disk size, which are useful when identifying multiple disks. See `lsblk --help` for a full list of supported columns.

#### wipefs

This article or section needs expansion.

Reason: Why would you want to make signatures invisible for libblkid? (Discuss in Talk:Device file)

wipefs can list or erase file system, RAID or partition-table signatures (magic strings) from the specified device to make the signatures invisible for libblkid(3). It does not erase the file systems themselves nor any other data from the device.

See wipefs(8) for more information.

For example, to erase all signatures from the device `/dev/sdb` and create a signature backup `~/wipefs-sdb-offset.bak` file for each signature:

    # wipefs --all --backup /dev/sdb

## Pseudo-devices

Device nodes that do not have a physical device.

- /dev/random, see random(4)
- /dev/shm
- /dev/null, /dev/zero, see null(4)
- /dev/full, see full(4)
- /dev/ttyX, where X is a number

## See also

- Linux allocated devices — The Linux Kernel documentation
- Gentoo:Device file

Category:

- System administration

Hidden category:

- Pages or sections flagged with Template:Expansion