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Cómo configurar fstab y lilo.conf con nombres persistentes

¿Alguna vez ha tenido el orden de cambio de sus unidades / dev / sda y / dev / sdb? ¿Conectar un dispositivo USB antes de arrancar su computadora causó un pánico en el kernel? ¿Con frecuencia desenchufa o conecta dispositivos nuevos en su computadora, cambiando así el orden de los nombres de los dispositivos? Si ha respondido afirmativamente a alguno de ellos, podría ser un buen candidato para utilizar nombres persistentes en su gestor de arranque y fstab.

¿Qué es el nombramiento persistente?

La denominación persistente le permite hacer referencia a su unidad por algo que no cambia. Hay varios métodos diferentes disponibles para la asignación de nombres persistentes y cubriremos lo siguiente: ID, etiqueta y UUID, así como PartLabel y PartUUID basados en GPT. Las más utilizadas son las etiquetas y los UUID, principalmente porque han existido durante mucho tiempo. Las tablas de partición GPT introdujeron una versión actualizada de etiquetas y UUID denominados partlabel y partuuid que se almacenan directamente en la tabla de partición. Sin embargo, comenzando con el kernel 3.8, PartUUID se ha expandido para generar identificadores únicos más cortos (UID) para las particiones MBR, permitiendo esencialmente que las unidades MBR usen PARTUUID.

Ahora, vamos a profundizar en los diversos métodos:

ID

/dev/disk/by-id/ es una carpeta generada dinámicamente bajo el sistema de archivos /dev/ . Esto cambiará dependiendo de los dispositivos que estén conectados a la computadora. Las identificaciones generalmente están compuestas por el número de modelo del disco duro, el número de serie y las particiones específicas. ls -la /dev/disk/by-id/ mostrará todos los ID y el dispositivo al que apunta bajo el sistema de archivos /dev/ (por ejemplo, /dev/sda , /dev/sdc3 , etc).

slackware@darkstar:~$ ls -la /dev/disk/by-*
/dev/disk/by-id:
total 0
drwxr-xr-x 2 root root 680 Jul 31 13:17 ./
drwxr-xr-x 8 root root 160 Jul 31 13:17 ../
lrwxrwxrwx 1 root root 9 Jul 31 17:18 ata-Crucial_CT480M500SSD1_13440956798B -> ../../sda
lrwxrwxrwx 1 root root 10 Jul 31 17:18 ata-Crucial_CT480M500SSD1_13440956798B-part1 -> ../../sda1
lrwxrwxrwx 1 root root 10 Jul 31 17:18 ata-Crucial_CT480M500SSD1_13440956798B-part2 -> ../../sda2
lrwxrwxrwx 1 root root 10 Jul 31 17:18 ata-Crucial_CT480M500SSD1_13440956798B-part3 -> ../../sda3
lrwxrwxrwx 1 root root 9 Jul 31 17:18 ata-WDC_WD1001FALS-00J7B1_WD-WMATV1953756 -> ../../sdb
lrwxrwxrwx 1 root root 10 Jul 31 17:18 ata-WDC_WD1001FALS-00J7B1_WD-WMATV1953756-part1 -> ../../sdb1
lrwxrwxrwx 1 root root 9 Jul 31 17:18 ata-WDC_WD40EZRX-00SPEB0_WD-WCC4E1021582 -> ../../sdc
lrwxrwxrwx 1 root root 10 Jul 31 17:18 ata-WDC_WD40EZRX-00SPEB0_WD-WCC4E1021582-part1 -> ../../sdc1

Por lo tanto, si siempre desea hacer referencia a la unidad Crucial (solo la unidad, no las particiones dentro de ella), puede usar el nombre de archivo /dev/disk/by-id/ ata- Crucial_CT480M500SSD1_13440956798B . (Verá un ejemplo de esto en la sección lilo.conf a continuación). Esto siempre apuntará a esa unidad, independientemente de si es /dev/sda o /dev/sdq . Para hacer referencia a una partición específica, simplemente haga coincidir el nombre del dispositivo actual ( /dev/sdb1 ) con su ID asociado, /dev/disk/by-id/ ata-WDC_WD40EZRX-00SPEB0_WD-WCC4E1050616-part1 .

Label

Las etiquetas (label) son un nombre opcional configurado por el usuario para la unidad. La mayoría de los sistemas de archivos admiten esto, pero no siempre se crean automáticamente. Todas las etiquetas se pueden encontrar en /dev/disk/by-label/ y se pueden ver fácilmente usando ls -la /dev/disk/by-label / .

/dev/disk/by-label:
total 0
drwxr-xr-x 2 root root 80 Jul 31 13:17 ./
drwxr-xr-x 8 root root 160 Jul 31 13:17 ../
lrwxrwxrwx 1 root root 10 Jul 31 17:18 Backup -> ../../sdc1
lrwxrwxrwx 1 root root 10 Jul 31 17:18 Data -> ../../sdb1

Las etiquetas pueden ser bastante convenientes sobre las ID debido a su capacidad para ser extremadamente cortas y memorables. Sin embargo, si no tiene cuidado o si mueve los discos entre sistemas, puede tener problemas con nombres duplicados que causan conflictos. Tanto lilo como fstab admiten el uso de LABEL = “Backup 'para hacer referencia directamente a la unidad en lugar de tener que usar' '/dev/disk/by-label/ Backup' ', lo que hace que esta sea una opción mucho más sencilla para hacer referencia a las unidades.

Si desea agregar una etiqueta a su partición, ArchWiki esta página tiene instrucciones para la mayoría de los sistemas de archivos.

UUID

UUIDs (Universally Unique IDentifiers) are a unique identifier generated for a partition. All Linux filesystems will generate UUIDs when they're formatted. FAT and NTFS filesystems do not support UUIDs, however, a short UID is used in place of a regular UUID. All UUIDs can be found under /dev/disk/by-uuid/ and can be viewed using ls -la /dev/disk/by-uuid/

/dev/disk/by-uuid:
total 0
drwxr-xr-x 2 root root 200 Jul 31 13:17 ./
drwxr-xr-x 8 root root 160 Jul 31 13:17 ../
lrwxrwxrwx 1 root root 10 Jul 31 17:18 226f1db3-2f14-4862-9998-8be1e8f7cdc9 -> ../../sda3
lrwxrwxrwx 1 root root 10 Jul 31 17:18 23bce2c2-996d-449e-89cc-0e5029cc6d8d -> ../../sda2
lrwxrwxrwx 1 root root 10 Jul 31 17:18 bc4538e5-9387-4e5c-877b-d15744acb6ce -> ../../sda1
lrwxrwxrwx 1 root root 10 Jul 31 17:18 cd554cf8-c346-4bd5-ba6a-84ac99af571f -> ../../sdc1
lrwxrwxrwx 1 root root 10 Jul 31 17:18 2ef6e776-c2eb-4e56-bc7e-dfe083559d8f -> ../../sdb1
lrwxrwxrwx 1 root root 10 Jul 31 17:18 126AC3506AC32EF3 -> ../../sdq1                      #Example NTFS UID -- not really in my system

UUIDs can also be referenced by using just UUID=226f1db3-2f14-4862-9998-8be1e8f7cdc9 in your /etc/lilo.conf and /etc/fstab files.

GPT (PartLabel and PartUUID)

The MBR (Master Boot Record) has been the primary partition table for harddrives for the past few decades (it was introduced in 1983). However, it is unable to be used on disks larger than 2TBs. That is where GPT (GUID Partition Table) comes in. This was developed as part of the UEFI spec but can be used without using UEFI.

In addition to the limitations of the MBR, there are also limitations of using UUIDs and Labels, mainly being that if you use those in your bootloader, you are required to use an initrd. While it is recommended by Pat to use an initrd, many users prefer using a kernel that doesn't require one (either using the huge kernel or building a custom kernel with the required hardware support compiled in). The GPT spec added PartLabel and PARTUUID as a way to save that information directly to the partition table (the “part” stands for partition). While both PartLabel and PartUUID are included in the GPT spec, the kernel only supports booting PARTUUIDs, so you can't use PartLabel in your bootloaders. If you want to use PartUUID, you don't need any initrd to be able to read this data, which makes it much easier to use on systems that aren't already using an initrd. Initially, since PARTUUID was introduced as part of the GPT spec, MBR-based devices could not be referenced using PARTUUID; however, basic support for PartUUID on MBR partitions was added starting with the 3.8 Linux kernel, so now any drive can be referenced by its “PARTUUID”.

PartLabel

This is almost identical to the regular Label option. It is located under /dev/disk/by-partlabel/ and can be viewed with ls -la /dev/disk/by-partlabel. PARTLABEL can only be used in the fstab. Due to lack of support in the kernel, you will need to use one of the other persistent naming conventions in your lilo.conf

/dev/disk/by-partlabel:
total 0
drwxr-xr-x 2 root root 60 Jul 31 17:18 ./
drwxr-xr-x 8 root root 160 Jul 31 13:17 ../
lrwxrwxrwx 1 root root 10 Jul 31 17:18 Linux\\x20filesystem -> ../../sdc1

Also, this will only show official PARTLABELs. It will not show any labels from disks using MBR. If you need to view those, you can use blkid.

slackware@darkstar:~$ su -
Password:
root@darkstar:~# blkid
/dev/sdc1: LABEL="Backup" UUID="cd554cf8-c346-4bd5-ba6a-84ac99af571f" TYPE="ext4" PARTLABEL="Linux filesystem" PARTUUID="62c372af-e868-4571-8ab4-db612c0fb38f"
/dev/sdb1: LABEL="Data" UUID="2ef6e776-c2eb-4e56-bc7e-dfe083559d8f" TYPE="ext4" PARTUUID="71b70c68-01"
/dev/sda1: UUID="bc4538e5-9387-4e5c-877b-d15744acb6ce" TYPE="swap" PARTUUID="6f47c81b-01"
/dev/sda2: UUID="23bce2c2-996d-449e-89cc-0e5029cc6d8d" TYPE="ext4" PARTUUID="6f47c81b-02"
/dev/sda3: UUID="226f1db3-2f14-4862-9998-8be1e8f7cdc9" TYPE="ext4" PARTUUID="6f47c81b-03"

As you can see in the case of /dev/sdc1, you can have a different LABEL and PARTLABEL. That is because these are stored independently of one another. LABEL is a filesystem trait, whereas PARTLABEL is a partition trait. Also note, based on how I created my filesystem, it has a generic “Linux filesystem” PARTLABEL, so if I were to create a new filesystem on a new drive without changing anything, I would have two drives with the same PARTLABEL. This is not an issue unless you try to reference the disk as a PARTLABEL.

If you want to add or change your PARTLABEL, you can do so using gdisk or cgdisk.

PartUUID

This is similar to PartLabel in that it is almost identical to it's not-“Part” counterpart (regular UUID). This UUID is generated automatically whenever you create/resize/move a partition. This will be a different UUID than the one provided by the filesystem. All PartUUIDs can be found under /dev/disk/by-partuuid/ and can be viewed using ls -la /dev/disk/by-partuuid/.

/dev/disk/by-partuuid:
total 0
drwxr-xr-x 2 root root 120 Jul 31 13:17 ./
drwxr-xr-x 8 root root 160 Jul 31 13:17 ../
lrwxrwxrwx 1 root root 10 Jul 31 17:18 468a6e66-39e3-4072-8997-0550dd12ad8e -> ../../sdb1

As you can see, this is just like PartLabel in that it only shows official PartUUIDs on GPT disks. If you need to view the system generated PartUUID for MBR partitions, you need to use blkid.

slackware@darkstar:~$ su -
Password:
root@darkstar:~# blkid
/dev/sdc1: LABEL="Backup" UUID="cd554cf8-c346-4bd5-ba6a-84ac99af571f" TYPE="ext4" PARTLABEL="Linux filesystem" PARTUUID="62c372af-e868-4571-8ab4-db612c0fb38f"
/dev/sdb1: LABEL="Data" UUID="2ef6e776-c2eb-4e56-bc7e-dfe083559d8f" TYPE="ext4" PARTUUID="71b70c68-01"
/dev/sda1: UUID="bc4538e5-9387-4e5c-877b-d15744acb6ce" TYPE="swap" PARTUUID="6f47c81b-01"
/dev/sda2: UUID="23bce2c2-996d-449e-89cc-0e5029cc6d8d" TYPE="ext4" PARTUUID="6f47c81b-02"
/dev/sda3: UUID="226f1db3-2f14-4862-9998-8be1e8f7cdc9" TYPE="ext4" PARTUUID="6f47c81b-03"

For non-GPT filesystems, the PARTUUID is generated from the Disk Identifier, followed by the partition number. You can view your Disk Identifier using fdisk.

root@darkstar:~# fdisk -l /dev/sda | grep identifier
Disk identifier: 0x6f47c81b
Due to the newness of GPT support, lilo does not have direct support of calling it, rather you need to use an addappend option (see the lilo.conf section below for further information). For PartUUIDs on MBR disks, the only time they'll change is if additional partitions are created. Keep that in mind if you're using them in your fstab and/or lilo.conf.

fstab

Your /etc/fstab is the easiest file to change. You simply replace any entries that pointed to your device names with TYPE=value (TYPE can be LABEL, UUID, PARTLABEL, PARTUUID). The original device names are listed as comments for your reference, they don't need to be in the final file. (Personally, since I like it to look nice and neat, I will make everything spaced out evenly.)

slackware@darkstar:~$ cat /etc/fstab
# /dev/sda1
UUID=bc4538e5-9387-4e5c-877b-d15744acb6ce      swap            swap    defaults,discard                     0 0
# /dev/sda2
UUID=23bce2c2-996d-449e-89cc-0e5029cc6d8d      /               ext4    defaults,noatime,discard             0 1
# /dev/sda3
PARTUUID="6f47c81b-03"                         /home           ext4    defaults,noatime,discard             0 2
# /dev/sdb1
LABEL=Data                                     /share/Data     ext4    defaults                             0 2
# /dev/sdc1
PARTLABEL="Linux filesystem"                   /share/Backup   ext4    defaults                             0 2

#/dev/cdrom                                    /mnt/cdrom      auto    noauto,owner,ro,comment=x-gvfs-show  0 0
devpts                                         /dev/pts        devpts  gid=5,mode=620                       0 0
proc                                           /proc           proc    defaults                             0 0
tmpfs                                          /dev/shm        tmpfs   defaults                             0 0

lilo.conf

Your /etc/lilo.conf takes a bit more finesse to change. Not everything is properly supported like the fstab options, so we need to throw in a few workarounds, depending on what you want to use.

To start out, we need to set up the top of your /etc/lilo.conf. This mainly includes the boot entry. This is what lilo uses to determine where to write the bootloader code into the partition table. This is only referenced when you run lilo to install the bootloader, so it won't be as affected as other drives if they're moved. However, if you've already taken the time to get this far, you might as well ensure you don't run into any issues by referencing your drive using persistent naming.

To do this, we would need to replace /dev/sda (or whatever your default boot drive is) with a reference that doesn't change. Since we need to reference the drive itself, and not any specific partitions, we need to use the ID method. Once you find the disk ID for your main drive, replace your boot with the full path to the ID. (NOTE: the original /dev/sda is commented out and only there for reference, you don't need to keep it.)

#boot = /dev/sda
boot = /dev/disk/by-id/ata-Crucial_CT480M500SSD1_13440956798B

Once you have the boot portion set up, you can then move onto the root partitions for your OSes.

LABEL and UUID

To use Labels and UUIDs, you need to use an initrd. It won't work without it. Since PARTLABEL in your lilo.conf isn't supported, if you want to use a label there, you will have to use this method. When building your initrd, you need to make sure you pass the -r option to specify your root partition, and set it to either your label or UUID. You can use the /usr/share/mkinitrd/mkinitrd_command_generator.sh script, although, if you're building it for a kernel version that you're not currently running (but have installed), make sure you pass the kernel version you intend to use to the script using the -k option. It will then spit out a mkinitrd command you can use, which you would just need to adjust the -r option.

root@darkstar:~# /usr/share/mkinitrd/mkinitrd_command_generator.sh -k 4.4.14
#
# mkinitrd_command_generator.sh revision 1.45
#
# This script will now make a recommendation about the command to use
# in case you require an initrd image to boot a kernel that does not
# have support for your storage or root filesystem built in
# (such as the Slackware 'generic' kernels').
# A suitable 'mkinitrd' command will be:

mkinitrd -c -k 4.4.14 -f ext4 -r /dev/sda2 -m jbd2:mbcache:ext4 -u -o /boot/initrd.gz

root@darkstar:~# blkid
/dev/sda2: UUID="25a4dafe-bbf2-413f-a60c-8c38efc0a122" TYPE="ext4" PARTUUID="1ae0ebfe-02"
/dev/sda1: UUID="d21b5f69-6d0c-48fb-b67c-912ebb0fd18e" TYPE="swap" PARTUUID="1ae0ebfe-01"

root@darkstar:~# mkinitrd -c -k 4.4.14 -f ext4 -r "UUID=25a4dafe-bbf2-413f-a60c-8c38efc0a122" -m jbd2:mbcache:ext4 -u -o /boot/initrd-4.4.14.gz
OK: /lib/modules/4.4.14/kernel/fs/jbd2/jbd2.ko added.
OK: /lib/modules/4.4.14/kernel/fs/mbcache.ko added.
OK: /lib/modules/4.4.14/kernel/fs/jbd2/jbd2.ko added.
OK: /lib/modules/4.4.14/kernel/fs/mbcache.ko added.
OK: /lib/modules/4.4.14/kernel/fs/ext4/ext4.ko added.
35942 blocks
/boot/initrd-4.4.14.gz created.
Be sure to run lilo again if you use it.
root@darkstar:~#

As you'll notice, the command provided by mkinitrd uses /dev/sda2 as the root drive, so we need to change that to match the UUID of the drive before running the mkinitrd command. By default, it will output the /boot/initrd.gz file, but I prefer to call mine based on the kernel version (which is helpful to ensure you don't overwrite a known-good initrd). When including the root partition in your initrd, it can be removed from lilo, since it won't use it (however, I've left it in but commented it out for visual reference).

Once you generate an initrd, you need to reference it in your stanza. I don't have any labels set for my primary drive, so I added an example that is commented out. You can use one or the other. As before, I commented out the original device, but it doesn't have to remain in the conf file.

Instead of changing your original stanza, it might be beneficial to keep it there in case you accidentally screw something up and your system doesn't boot, then you can just select your original config and go and fix things and try it again. Once you have verified your system boots properly with your new stanza, if desired, you can remove the old one.
image = /boot/vmlinuz-generic-3.10.17
initrd = /boot/initrd-3.10.17.gz
#root = /dev/sda2
#root = "UUID=23bce2c2-996d-449e-89cc-0e5029cc6d8d"
#root = "LABEL=Mylabelhere"
label = Slack-generic
read-only

image = /boot/vmlinuz
root = /dev/sda2
label = Slack-default
read-only

PARTUUID

Now, as mentioned above, PARTUUID does not require an initrd (although, it works fine if you do use one). However, lilo is old enough that it doesn't have proper support for it, so there is a workaround to get it working. Instead of referencing root like we did above, we need to replace the root option within an “addappend”. This will add anything extra to the initial append line at the top of lilo.conf. Keep in mind your spaces, as it will be placed directly afterwards, so it might be wise to include an extra space at the beginning of the line to ensure it doesn't accidentally combine words (which would likely cause a kernel panic and prevent you from booting). For me, since my root partition is on a drive with an MBR, I'll have the shortened PARTUUID instead of the regular 32 character length of a proper PARTUUID.

image = /boot/vmlinuz-generic
addappend = " root=PARTUUID=6f47c81b-02"
label = Slack-partuuid
read-only

image = /boot/vmlinuz-generic
initrd = /boot/initrd-4.4.14.gz
root = "UUID=25a4dafe-bbf2-413f-a60c-8c38efc0a122"
label = Slack-UUID
read-only

image = /boot/vmlinuz-huge
root = /dev/sda2
label = Slack-default
read-only

As noted above, PARTLABEL is not supported with lilo.

Finishing Up

Once you have your /etc/lilo.conf file updated, we should test it to make sure there aren't any glaring errors. Lilo has the ability to test a config using the -t option.

root@darkstar:~# lilo -t
Warning: LBA32 addressing assumed
Added Slack-partuuid  +  *
Added Slack-UUID  +
Added Slack-default  +
The boot sector and the map file have *NOT* been altered.
One warning was issued.

The LBA32 warning is normal with Slackware's lilo.conf and can be ignored (however, you can get rid of it by added LBA32 in the Global section of your lilo.conf). The main thing we're looking for is that all of our stanzas were added and no errors were issued. If that worked, then we can run lilo by itself to finish the process.

root@darkstar:~# lilo
Warning: LBA32 addressing assumed
Added Slack-partuuid  +  *
Added Slack-UUID  +
Added Slack-default  +
One warning was issued.

If you got this far, go ahead and reboot. Your system should now no longer rely on device names that can easily change.

Final thing to remember, is your device names can change at any time. As should always be the case, whether or not you're using persistent names, before you do anything that may wipe a drive (e.g. dd, fdisk, etc), ensure you are using the correct drive name. You don't want to assume your thumbdrive is /dev/sdc (because that's what it's always been) before using dd to write that shiny new Slackware64-current iso on there. If your device names have changed, you could be writing that iso to your root partition and take out your whole OS. Use the tools provided above (the various folders under /dev/disk/, blkid, and/or dmesg) to verify what device name you want to use before running the command.

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