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Konstantin
Asked: 2024-03-17 18:03:22 +0800 CST

Device the file or directory resides on

  • 772

How to identify the device on which the file or directory resides?

There is a stat module.
Among the results there is a "Device the inode resides on".

How can you map the "Device the inode resides on" to a partition?

ansible

2 Answers

  1. Best Answer

    First one need to understand What is the device of inode? and device number in stat command output.

    Then, for an example debug output

    TASK [debug] *****
ok: [localhost] =>
  result:
    changed: false
    failed: false
    stat:
...
      dev: 2051

    there is a Device ID with 2051 decimal but we would need it in HEX. According How can I convert a decimal string to an hexadecimal string? a task like

      - debug:
      msg: "{{ '%#x' % result.stat.dev }}"

    would report

    TASK [debug] *****
ok: [localhost] =>
  msg: '0x803'

    This needs to be split into major (8) and minor (3) device. Maybe start with

    "{{ ('%#x' % result.stat.dev).split('x') | last }}"

    In an other task it would be necessary to gather the result of

    ~/test$ ls -al /dev/sd*
brw-rw----. 1 root disk 8,  0 Feb 29 00:01 /dev/sda
brw-rw----. 1 root disk 8,  1 Feb 29 00:01 /dev/sda1
brw-rw----. 1 root disk 8,  2 Feb 29 00:01 /dev/sda2
brw-rw----. 1 root disk 8,  3 Feb 29 00:01 /dev/sda3
brw-rw----. 1 root disk 8,  4 Feb 29 00:01 /dev/sda4
brw-rw----. 1 root disk 8,  5 Feb 29 00:01 /dev/sda5
brw-rw----. 1 root disk 8, 16 Feb 29 00:01 /dev/sdb
brw-rw----. 1 root disk 8, 32 Feb 29 00:01 /dev/sdc
brw-rw----. 1 root disk 8, 33 Feb 29 00:01 /dev/sdc1

    and parse it accordingly since ansible_facts.device_links ansible_facts.devices do not collect and hold that kind of information.

    Depending on the infrastructure lsblk --output formatted for necessary information only might be easier.

    lsblk -o NAME,MAJ:MIN,MOUNTPOINT
NAME   MAJ:MIN MOUNTPOINT
sda      8:0
├─sda1   8:1   /boot/efi
├─sda2   8:2   /boot
├─sda3   8:3   /
├─sda4   8:4   /tmp
└─sda5   8:5   [SWAP]
sdb      8:16  /var/lib/pgsql/16/data
sdc      8:32
└─sdc1   8:33  /var
sr0     11:0

    Or according How to get a device/partition name of a file? just

    cat /proc/partitions
major minor  #blocks  name

  11        0    1234567 sr0
   8       32   12345678 sdc
   8       33   12345678 sdc1
   8        0  123456789 sda
   8        1     123456 sda1
   8        2     123456 sda2
   8        3   12345678 sda3
   8        4   12345678 sda4
   8        5    1234567 sda5
   8       16    1234567 sdb

    From here we can see Major 8 (SCSI) and Minor 3 is /dev/sda3. And "How to find out what's behind the major number?", see in example Linux : Major and Minor device numbers or Major and minor numbers of a partition.

    An example task with zero padded fields from text file

      - name: Gather Custom Fact - Partition major minor numbers
    shell:
      cmd: |
        tail -n +3 /proc/partitions | awk '{ printf "%s: %02i%02i\n", $4,$1,$2 }'
    check_mode: false
    changed_when: false
    register: partmajmin

  - debug:
      var: (partmajmin.stdout | from_yaml)

    will result into an output of

    TASK [debug] *********************
ok: [localhost] =>
  (partmajmin.stdout | from_yaml):
    sda: 0800
    sda1: 0801
    sda2: 0802
    sda3: 0803
    sda4: 0804
    sda5: 0805
    sdb: 0816
    sdc: 0832
    sdc1: 0833
    sr0: 1100

    The numbers are accessible as well transformable into integer in example as follow

      - debug:
      var: (partmajmin.stdout | from_yaml).sda3 | int(base=16)

    resulting into an output of

    TASK [debug] ************************************************
ok: [localhost] =>
  (partmajmin.stdout | from_yaml).sda3 | int(base=16): '2051'

    Finally, a task

      - name: Device an inode can reside on
    debug:
      msg: "{{ item.key }}"
    loop: "{{ lookup('dict', (partmajmin.stdout | from_yaml)) }}"
    loop_control:
      label: "{{ item.value | int(base=16) }}"

    will report

    TASK [Device an inode can reside on] ******
ok: [localhost] => (item=2099) =>
  msg: sdc1
ok: [localhost] => (item=2098) =>
  msg: sdc
ok: [localhost] => (item=2052) =>
  msg: sda4
ok: [localhost] => (item=1100) =>
  msg: sr0
ok: [localhost] => (item=2053) =>
  msg: sda5
ok: [localhost] => (item=2050) =>
  msg: sda2
ok: [localhost] => (item=2048) =>
  msg: sda
ok: [localhost] => (item=2070) =>
  msg: sdb
ok: [localhost] => (item=2049) =>
  msg: sda1
ok: [localhost] => (item=2051) =>
  msg: sda3
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  2. supplement: for a minor number must take the last two digits of the number

    File: /path/to/file1
    linux stat: device 8/1
    ansible device stat: dev: 2049

    2049 (DEC) = 801 (HEX) --> 8.01 --> 8/01 (HEX) = 8/1 (DEC)

    File: /path/to/file2
    linux stat: device 259/2
    ansible device stat: dev: 66306

    66306 (DEC) = 10302 (HEX) --> 103.02 --> 103/02 (HEX) = 259/2 (DEC)

    File: /path/to/file3
    linux stat: device 254/1
    ansible device stat: dev: 65025

    65025 (DEC) = FE01 (HEX) --> FE.01 --> FE/01 (HEX) = 254/1 (DEC)

    File: /path/to/file4
    linux stat: device 0/45
    ansible device stat: dev: 45

    45 (DEC) = 2D (HEX) --> 0.2D --> 0/2D (HEX) = 0/45 (DEC)

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