Exercise: Create file systems and mount them

Create file systems and mount them

• Create xfs and ext4 file systems and swap space.
• Mount, use and unmount file systems.
• Read UUIDs and diagnose a busy mount.

Start the exercise

On workstation, start the exercise. It partitions the spare disk /dev/sdb of servera into the three partitions of the previous exercise (data 1 GiB, logs 1 GiB, swap 512 MiB).

[student@workstation ~]$ lab start sa-filesystems

Later tasks assume that you are logged in to the server they name: ssh student@servera from workstation, then sudo -i for a root shell.

Create the file systems and the swap area

Make an XFS file system on sdb1, an ext4 file system labelled logs on sdb2, and swap space on sdb3. Show their UUIDs and types.

[root@servera ~]# mkfs.xfs /dev/sdb1
meta-data=/dev/sdb1              isize=512    agcount=4, agsize=65536 blks
...output omitted...
[root@servera ~]# mkfs.ext4 -L logs /dev/sdb2
...output omitted...
[root@servera ~]# mkswap /dev/sdb3
Setting up swapspace version 1, size = 512 MiB (536866816 bytes)
no label, UUID=89858a47-2255-4fa3-a2a9-64711ac2d782
[root@servera ~]# blkid -s UUID -s TYPE /dev/sdb1 /dev/sdb2 /dev/sdb3
/dev/sdb1: UUID="c64946eb-fc27-4485-8020-db4119b686eb" TYPE="xfs"
/dev/sdb2: UUID="cd0b3883-1d6d-4271-a89e-2f48a2dac5b7" TYPE="ext4"
/dev/sdb3: UUID="89858a47-2255-4fa3-a2a9-64711ac2d782" TYPE="swap"

Write down (or copy) the UUIDs: they will be different on your machine.

Mount and use them

Create /data and /logs, mount the file systems on them, and compare sizes and types with df. Create a file in each.

[root@servera ~]# mkdir -p /data /logs
[root@servera ~]# mount /dev/sdb1 /data
[root@servera ~]# mount /dev/sdb2 /logs
[root@servera ~]# df -hT /data /logs
Filesystem     Type  Size  Used Avail Use% Mounted on
/dev/sdb1      xfs   960M   39M  922M   5% /data
/dev/sdb2      ext4  974M   24K  907M   1% /logs
[root@servera ~]# echo hello > /data/a.txt; echo world > /logs/b.txt
[root@servera ~]# lsblk -f /dev/sdb
NAME   FSTYPE FSVER LABEL UUID                                 FSAVAIL FSUSE% MOUNTPOINTS
sdb
├─sdb1 xfs                c64946eb-fc27-4485-8020-db4119b686eb  921M     4% /data
├─sdb2 ext4   1.0   logs  cd0b3883-1d6d-4271-a89e-2f48a2dac5b7  906.2M     0% /logs
└─sdb3 swap   1           89858a47-2255-4fa3-a2a9-64711ac2d782

Sizes are slightly smaller than 1 GiB because the file systems keep some space for their own structures. ext4 reserves some more than XFS.

A busy mount

Change into /data and try to unmount it. Then find out who is using it, leave the directory, and unmount and mount it again.

[root@servera ~]# cd /data
[root@servera data]# umount /data
umount: /data: target is busy.
[root@servera data]# fuser -vm /data
                     USER        PID ACCESS COMMAND
/data:               root     kernel mount /data
                     root        713 ..c.. bash
[root@servera data]# cd /
[root@servera /]# umount /data && echo unmounted
unmounted
[root@servera /]# mount /dev/sdb1 /data && ls /data
a.txt

The only user was your own shell (access c = current directory). The data survived the unmount, of course.

Use swap

Enable the swap partition and compare free -h before and after. Then disable it again.

[root@servera /]# free -h | tail -1
Swap:             0B          0B          0B
[root@servera /]# swapon /dev/sdb3
[root@servera /]# swapon --show
NAME      TYPE      SIZE USED PRIO
/dev/sdb3 partition 512M   0B   -2
[root@servera /]# free -h | tail -1
Swap:          511Mi          0B       511Mi
[root@servera /]# swapoff /dev/sdb3

Leave the file systems mounted for the next exercise, or unmount them with umount /data /logs and start from the partitions again.

Grade and finish

Check your work with lab grade sa-filesystems, then put the exercise away with lab finish sa-filesystems.