What is uuid linux

Find UUID of Storage Devices in Linux

The UUID of a partition is required mainly for mounting the partitions correctly in a computer system where hundreds of hard drives are installed. If you mount the hard drives or SSDs using UUIDs, there is almost zero changes of the wrong hard drive getting mounted and causing serious data loss.

Our usual computers and laptops where mostly 1 or 2 hard drives are installed and we need limited number of partitions won’t benefit much from UUIDs.

In this article, I will show you how to find the UUID of storage devices such as hard drive or SSD partitions in Linux. So, let’s get started.

Finding UUID with blkid:

You can find the UUID of all the disk partitions on your Linux system with the blkid command. The blkid command is available by default on most modern Linux distributions.

To find the UUIDs of your disk partitions, run the following command:

As you can see, the filesystems that has UUID are displayed. A lot of loop devices are also listed.

In the earlier output, you have seen a lot of unnecessary loop devices. If you want to only list the filesystems that has UUID set, you may filter the output of the blkid command as follows:

You should be able to get a clean filtered output. Only the filesystems that has UUID set are listed.

Finding UUID with ls:

In Linux, all the devices including the storage devices are represented as files. So, the partitions with UUID set are also represented as files. You can list all these files with the ls command.

To list all the partitions and their UUIDs, run the following command:

As you can see, the partition name (i.e. sda1, sda2) and their UUIDs are listed.

Finding UUID with lsblk:

You can also list the UUID of your partitions with the lsblk command:

For example, to list UUID of your partitions with the lsblk command, run lsblk as follows:

As you can see, the UUIDs of the partitions are listed.

You can filter out all the loop devices to make the output cleaner as well. To do that, run the lsblk command as follows:

As you can see, only the partitions with UUID are listed. The output is now much cleaner.

Where to Go Next:

Now that you know how to find the UUID of the storage devices in Linux, you can learn how to mount the partitions with UUID. I have written a dedicated article on how to mount partitions with UUID using the /etc/fstab file. You can read it at https://linuxhint.com/mount_partition_uuid_label_linux/

So, that’s how you find the UUID of storage devices in Linux. Thanks for reading this article.

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UUIDs and Linux: Everything you ever need to know [Update]

What is so special about UUIDs in Linux? I don’t know! But here is everything you ever need to know about UUIDs on Linux.

A single, simple short tip about looking up UUIDs in Linux from 2007 is one of the most successful posts I ever wrote. And is still looked up by hundreds each day! So I decided: Feed the masses.

This list covers everything about Linux and UUIDs. And it is feature complete. Of course. *cough*

Background

UUIDs are 128 bit long numbers represented by 32 hexadecimal digits and which are used in software development to uniquely identify information with no further context. They are described in RFC 4122, an example UUID is:

UUIDs are probably best known in Linux as identifier for block devices. The Windows world knows UUIDs in the form of Microsoft’s globally unique identifiers, GUID, which are used in Microsoft’s Component Object Model.

The UUIDs are generated in various variants: originally most of them were derived from the Computer’s MAC, later hash sums of names were used. And about the question, how many UUIDs there are and how big the chance is that you will generate a a number you already own, here are some numbers from Wikipedia’s UUID article:

After generating 1 billion UUIDs every second for the next 100 years, the probability of creating just one duplicate would be about 50%. The probability of one duplicate would be about 50% if every person on earth owns 600 million UUIDs.

Usage in fstab

As mentioned UUIDs are most often used in Linux to identify block devices. Imagine, you have a couple of hard disks attached via USBs, than there is no persistent, reliable naming of the devices: sometimes the first USB hard disk is named “sda”, sometimes it is named “sdb”. So to uniquely address the right disk for example in your /etc/fstab , you have to add an entry like:

For the block device itself, the uuid is stored in the superblock.

Beware however that UUIDs should not be used in fstab when you work with LVM snapshots. See the section “When not to use them” below for more details.

Linux implementation and generation

In Linux UUIDs are generated in /drivers/char/random.c?id=refs/tags/v3.8 , and you can generate new ones via proc:

There is also the library libuuid which is used by uuidgen and especially by the ext2/3/4 tools E2fsprogs to generate UUIDs:

How to get them, bash style

The most interesting part in UUIDs is most likely how to get the current UUIDs of the hard disks. As already mentioned years ago, there are two major ways to retrieve them: a simple ls call in a special directory, and the tool blkid .

So, first the ls call which has to be made in the directory /dev/disk/by-uuid . The directory contains links named after the UUIDs and pointing to the “real” block device files. Pretty handy if you are on a system where hardly anything is installed.

The second call uses the tool blkid which is part of the util-linux package. It provides a real interface to actually query for certain devices and also supports searching for labels.

And there are even more ways! Let’s install hwinfo :

As you see hwinfo lists huge amounts of data about your hardware – among them are the UUIDs of the devices. Use it when you are grabbing for more data about the block devices anyway.

Or how about udevadm? It is the udev provided tool for querying data from the udev database. This database contains all the information udev has about the system, so the UUID info is just one among many, many other data. If you are writing a “modern” script which integrates with Linux standard tools nicely, I guess I would go with udev. But for pure, quick and dirty command line utilization, it produces a bit too many information, just like hwinfo .

In this context the tool udevinfo is also mentioned sometimes. However, that is deprecated, most distributions don’t ship it anymore. Also, another often mentioned way to retrieve the UUIDs is the program /lib/vol/vol_id . But as described in bug redhat#476379 vol_id is only a private udev function. It should not be used by outside programs (or people) since the application interface is not stable. Also, the entire program might be removed in the future and in fact is already removed on some distributions.

Another tool which contains many disk data is dumpe2fs . It prints the super block and blocks group information for the selected filesystem and thus has also knowledge about the uuid:

Thanks to Greg for that tip!

And not to forget is lsblk which can has a nice structured output in the shell, providing not only the UUID but also the directory, available storage and so on. The advantage of this command is that it is very easy to identify which disk carries which UUID:

How to get them, GUI style

If you are afraid of shells, there is of course a KDE-GUI tool available as well to look up the UUID: /usr/bin/kcmshell4 devinfo

Setting a UUID

As mentioned in the comment section, it can be also interesting to set a UUID. Since the UUID is part of the superblock the way to set it depends on the used file system. For ext file systems you can use tune2fs :

When not to use them

As mentioned by Zhenech it is not always advisable to use UUIDs everywhere.

Since it is not possible to mount two file systems with the same UUID with most file systems, extra care need to be taken when LVM snapshots (or cloned disks) are used in an environment: mounting might fail due to duplicate UUIDs.

One way to deal with this is by the way to change the UUID during creation or afterwards, another way is to mount with the nouuid option.

Note that Btrfs is different here, since you might mount multiple sub-volumes, all of them from a different main UUID, as Ben pointed out.

Anything else

If you have any other, further information, please post them in the comments! I will happily add them here. After all, my years old short tip already got me 250 k visits, I wonder how many a comprehensive list will bring me…

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7 Methods to identify Disk Partition/FileSystem UUID in Linux

As a Linux administrator you should aware of that how do you check partition UUID or filesystem UUID.

Because most of the Linux systems are mount the partitions with UUID. The same has been verified in the /etc/fstab file.

There are many utilities available to check UUID. In this article we will show you how to check UUID in many ways and you can choose the one which is suitable for you.

What is UUID?

UUID stands for Universally Unique Identifier which helps Linux system to identify a hard drives partition instead of block device file.

libuuid is part of the util-linux-ng package since kernel version 2.15.1 and it’s installed by default in Linux system.

The UUIDs generated by this library can be reasonably expected to be unique within a system, and unique across all systems.

It’s a 128 bit number used to identify information in computer systems. UUIDs were originally used in the Apollo Network Computing System (NCS) and later UUIDs are standardized by the Open Software Foundation (OSF) as part of the Distributed Computing Environment (DCE).

UUIDs are represented as 32 hexadecimal (base 16) digits, displayed in five groups separated by hyphens, in the form 8-4-4-4-12 for a total of 36 characters (32 alphanumeric characters and four hyphens).

For example: d92fa769-e00f-4fd7-b6ed-ecf7224af7fa

Sample of my /etc/fstab file.

We can check this using the following seven commands.

• blkid Command: locate/print block device attributes.
• lsblk Command: lsblk lists information about all available or the specified block devices.
• hwinfo Command: hwinfo stands for hardware information tool and great utility that used to probe for the hardware present in the system.
• udevadm Command: udev management tool.
• tune2fs Command: adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems.
• dumpe2fs Command: dump ext2/ext3/ext4 filesystem information.
• Using by-uuid Path: The directory contains UUID and real block device files, UUIDs were symlink with real block device files.

How to check Disk Partition/FileSystem UUID in Linux using blkid Command?

blkid is a command-line utility to locate/print block device attributes. It uses libblkid library to get disk partition UUID in Linux system.

How to check Disk Partition/FileSystem UUID in Linux using lsblk Command?

lsblk lists information about all available or specified block devices. The lsblk command reads the sysfs filesystem and udev db to gather information.

If the udev db is not available or lsblk is compiled without udev support than it tries to read LABELs, UUIDs and filesystem types from the block device. In this case root permissions are necessary. The command prints all block devices (except RAM disks) in a tree-like format by default.

How to check Disk Partition/FileSystem UUID in Linux using by-uuid path?

The directory contains UUID and real block device files, UUIDs were symlink with real block device files.

How to check Disk Partition/FileSystem UUID in Linux using hwinfo Command?

hwinfo stands for hardware information tool is another great utility that used to probe for the hardware present in the system and display detailed information about varies hardware components in human readable format.

How to check Disk Partition/FileSystem UUID in Linux using udevadm Command?

udevadm expects a command and command specific options. It controls the runtime behavior of systemd-udevd, requests kernel events, manages the event queue, and provides simple debugging mechanisms.

How to check Disk Partition/FileSystem UUID in Linux using tune2fs Command?

tune2fs allows the system administrator to adjust various tunable filesystem parameters on Linux ext2, ext3, or ext4 filesystems. The current values of these options can be displayed by using the -l option.

How to check Disk Partition/FileSystem UUID in Linux using dumpe2fs Command?

dumpe2fs prints the super block and blocks group information for the filesystem present on device.

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Как узнать UUID диска в Linux

UUID или Universal Unique Identifier — это универсальный уникальный идентификатор, который может использоваться для однозначной идентификации определенного устройства компьютера. В операционных системах Linux UUID очень часто используется для идентификации разделов дисков в загрузчике Grub или в файле /etc/fstab. Это очень удобно, поскольку если вы извлечете диск или подключите его к другому разъему SATA, то его имя в системе изменится, а UUID останется прежнем.

Но у этого метода есть и недостаток. UUID рассчитывается на основе метаданных раздела или диска, поэтому если вы измените его размер, UUID тоже изменится, что приведет к поломке системы и вы не сможете загрузится. Исправить ситуацию можно только указав правильный UUID.

Как узнать UUID диска в Linux

Давайте разберем как узнать UUID диска в Linux. Все диски и разделы перечислены в виртуальном каталоге /dev/. Здесь есть подкаталог /dev/disk/by-uuid/ в котором вы можете посмотреть UUID идентификаторы всех подключенных к системе дисков. Для этого выполните:

ls -la /dev/disk/by-uuid/

Строки состоящие из большого количества цифр и букв, подсвеченные бирюзовым цветом и есть UUID.

2. blkid

Ещё для просмотра UUID можно использовать утилиту blkid. Её необходимо запускать от имени суперпользователя, но она показывает информацию только по нужному вам разделу. Например, чтобы посмотреть UUID раздела /dev/sda6 выполните:

sudo blkid /dev/sda6

Здесь UUID выводится в таком формате:

Эту строчку уже можно целиком вставлять в /etc/fstab или настройки загрузчика grub. Утилита позволяет посмотреть информацию для нескольких устройств:

sudo blkid /dev/sd*

3. lsblk

Ещё один вариант — эту утилита lsblk, которая тоже может показывать UUID:

lsblk -o +uuid,name

4. Графический интерфейс

Если вы не хотите использовать терминал, то всегда можете посмотреть UUID в графическом интерфейсе. Для этого используйте утилиту Gnome Disks. Её можно найти в главном меню операционной системы:

Для просмотра UUID просто выберите нужный жесткий диск и кликните по разделу, для которого нужно посмотреть информацию:

Выводы

UUID довольно часто используется при работе с разделами в Linux несмотря на то, что обычные имена разделов намного удобнее и проще запоминаются. Надеюсь, эта информация была полезной для вас.

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