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BLKID(8) System Administration BLKID(8) NAME blkid - locate/print block device attributes SYNOPSIS blkid --label label | --uuid uuid blkid [--no-encoding --garbage-collect --list-one --cache-file file] [--output format] [--match-tag tag] [--match-token NAME=value] [device...] blkid --probe [--offset offset] [--output format] [--size size] [--match-tag tag] [--match-types list] [--usages list] [--no-part-details] device... blkid --info [--output format] [--match-tag tag] device... DESCRIPTION The blkid program is the command-line interface to working with the lib- blkid(3) library. It can determine the type of content (e.g., filesystem or swap) that a block device holds, and also the attributes (tokens, NAME=value pairs) from the content metadata (e.g., LABEL or UUID fields). It is recommended to use lsblk(8) command to get information about block devices, or lsblk --fs to get an overview of filesystems, or findmnt(8) to search in already mounted filesystems. lsblk(8) provides more information, better control on output for- matting, easy to use in scripts and it does not require root per- missions to get actual information. blkid reads information di- rectly from devices and for non-root users it returns cached un- verified information. blkid is mostly designed for system services and to test libblkid(3) functionality. When device is specified, tokens from only this device are displayed. It is possible to specify multiple device arguments on the command line. If none is given, all partitions or unpartitioned devices which appear in /proc/partitions are shown, if they are recognized. blkid has two main forms of operation: either searching for a device with a specific NAME=value pair, or displaying NAME=value pairs for one or more specified devices. For security reasons blkid silently ignores all devices where the probing result is ambivalent (multiple colliding filesystems are detected). The low-level probing mode (-p) provides more information and extra exit status in this case. It's recommended to use wipefs(8) to get a detailed overview and to erase obsolete stuff (magic strings) from the device. OPTIONS The size and offset arguments may be followed by the multiplicative suf- fixes like KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is optional, e.g., "K" has the same meaning as "KiB"), or the suffixes KB (=1000), MB (=1000*1000), and so on for GB, TB, PB, EB, ZB and YB. -c, --cache-file cachefile Read from cachefile instead of reading from the default cache file (see the CONFIGURATION FILE section for more details). If you want to start with a clean cache (i.e., don't report devices previously scanned but not necessarily available at this time), specify /dev/null. -d, --no-encoding Don't encode non-printing characters. The non-printing characters are encoded by ^ and M- notation by default. Note that the --output udev output format uses a different encoding which cannot be disabled. -D, --no-part-details Don't print information (PART_ENTRY_* tags) from partition table in low-level probing mode. -g, --garbage-collect Perform a garbage collection pass on the blkid cache to remove devices which no longer exist. -H, --hint setting Set probing hint. The hints are an optional way to force probing func- tions to check, for example, another location. The currently supported is "session_offset=number" to set session offset on multi-session UDF. -i, --info Display information about I/O Limits (aka I/O topology). The 'export' output format is automatically enabled. This option can be used to- gether with the --probe option. -k, --list-filesystems List all known filesystems and RAIDs and exit. -l, --list-one Look up only one device that matches the search parameter specified with the --match-token option. If there are multiple devices that match the specified search parameter, then the device with the highest prior- ity is returned, and/or the first device found at a given priority (but see below note about udev). Device types in order of decreasing prior- ity are: Device Mapper, EVMS, LVM, MD, and finally regular block de- vices. If this option is not specified, blkid will print all of the de- vices that match the search parameter. This option forces blkid to use udev when used for LABEL or UUID tokens in --match-token. The goal is to provide output consistent with other utils (like mount(8), etc.) on systems where the same tag is used for multiple devices. -L, --label label Look up the device that uses this filesystem label; this is equal to --list-one --output device --match-token LABEL=label. This lookup method is able to reliably use /dev/disk/by-label udev symlinks (depen- dent on a setting in /etc/blkid.conf). Avoid using the symlinks di- rectly; it is not reliable to use the symlinks without verification. The --label option works on systems with and without udev. Unfortunately, the original blkid(8) from e2fsprogs uses the -L option as a synonym for -o list. For better portability, use -l -o device -t LABEL=label and -o list in your scripts rather than the -L option. -n, --match-types list Restrict the probing functions to the specified (comma-separated) list of superblock types (names). The list items may be prefixed with "no" to specify the types which should be ignored. For example: blkid --probe --match-types vfat,ext3,ext4 /dev/sda1 probes for vfat, ext3 and ext4 filesystems, and blkid --probe --match-types nominix /dev/sda1 probes for all supported formats except minix filesystems. This option is only useful together with --probe. -o, --output format Use the specified output format. Note that the order of variables and devices is not fixed. See also option -s. The format parameter may be: full print all tags (the default) value print the value of the tags list print the devices in a user-friendly format; this output format is unsupported for low-level probing (--probe or --info). This output format is DEPRECATED in favour of the lsblk(8) command. device print the device name only; this output format is always enabled for the --label and --uuid options udev print key="value" pairs for easy import into the udev environment; the keys are prefixed by ID_FS_ or ID_PART_ prefixes. The value may be modified to be safe for udev environment; allowed is plain ASCII, hex-escaping and valid UTF-8, everything else (including whitespaces) is replaced with '_'. The keys with _ENC postfix use hex-escaping for unsafe chars. The udev output returns the ID_FS_AMBIVALENT tag if more su- perblocks are detected, and ID_PART_ENTRY_* tags are always re- turned for all partitions including empty partitions. This output format is DEPRECATED. export print key=value pairs for easy import into the environment; this output format is automatically enabled when I/O Limits (--info op- tion) are requested. The non-printing characters are encoded by ^ and M- notation and all potentially unsafe characters are escaped. json Print the tags entries in JSON objects. -O, --offset offset Probe at the given offset (only useful with --probe). This option can be used together with the --info option. -p, --probe Switch to low-level superblock probing mode (bypassing the cache). Note that low-level probing also returns information about partition table type (PTTYPE tag) and partitions (PART_ENTRY_* tags). The tag names produced by low-level probing are based on names used internally by libblkid and it may be different than when executed without --probe (for example PART_ENTRY_UUID= vs PARTUUID=). See also --no-part-de- tails. -s, --match-tag tag For each (specified) device, show only the tags that match tag. It is possible to specify multiple --match-tag options. If no tag is speci- fied, then all tokens are shown for all (specified) devices. In order to just refresh the cache without showing any tokens, use --match-tag none with no other options. -S, --size size Override the size of device/file (only useful with --probe). -t, --match-token NAME=value Search for block devices with tokens named NAME that have the value value, and display any devices which are found. Common values for NAME include TYPE, LABEL, and UUID. If there are no devices specified on the command line, all block devices will be searched; otherwise only the specified devices are searched. -u, --usages list Restrict the probing functions to the specified (comma-separated) list of "usage" types. Supported usage types are: filesystem, raid, crypto and other. The list items may be prefixed with "no" to specify the us- age types which should be ignored. For example: blkid --probe --usages filesystem,other /dev/sda1 probes for all filesystem and other (e.g., swap) formats, and blkid --probe --usages noraid /dev/sda1 probes for all supported formats except RAIDs. This option is only use- ful together with --probe. -U, --uuid uuid Look up the device that uses this filesystem uuid. For more details see the --label option. -h, --help Display help text and exit. -V, --version Display version and exit. EXIT STATUS If the specified device or device addressed by specified token (option --match-token) was found and it's possible to gather any information about the device, an exit status 0 is returned. Note the option --match-tag fil- ters output tags, but it does not affect exit status. If the specified token was not found, or no (specified) devices could be identified, or it is impossible to gather any information about the device identifiers or device content an exit status of 2 is returned. For usage or other errors, an exit status of 4 is returned. If an ambivalent probing result was detected by low-level probing mode (-p), an exit status of 8 is returned. CONFIGURATION FILE The standard location of the /etc/blkid.conf config file can be overridden by the environment variable BLKID_CONF. The following options control the libblkid library: SEND_UEVENT=<yes|not> Sends uevent when /dev/disk/by-{label,uuid,partuuid,partlabel}/ symlink does not match with LABEL, UUID, PARTUUID or PARTLABEL on the device. Default is "yes". CACHE_FILE=<path> Overrides the standard location of the cache file. This setting can be overridden by the environment variable BLKID_FILE. Default is /run/blkid/blkid.tab, or /etc/blkid.tab on systems without a /run di- rectory. EVALUATE=<methods> Defines LABEL and UUID evaluation method(s). Currently, the libblkid library supports the "udev" and "scan" methods. More than one method may be specified in a comma-separated list. Default is "udev,scan". The "udev" method uses udev /dev/disk/by-* symlinks and the "scan" method scans all block devices from the /proc/partitions file. ENVIRONMENT Setting LIBBLKID_DEBUG=all enables debug output. AUTHORS blkid was written by Andreas Dilger for libblkid and improved by Theodore Ts'o and Karel Zak. SEE ALSO libblkid(3), findfs(8), lsblk(8), wipefs(8) REPORTING BUGS For bug reports, use the issue tracker <https://github.com/util-linux/util-linux/issues>. AVAILABILITY The blkid command is part of the util-linux package which can be downloaded from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils/util-linux/>. util-linux 2.42.2 2026-06-16 BLKID(8)
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | CONFIGURATION FILE | ENVIRONMENT | AUTHORS | SEE ALSO | REPORTING BUGS | AVAILABILITY
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