Rhcsa 01 - create partitions and file systems

Preface

This article demonstrates Create a loop file , And its Partition 、 format , and mount .

What is? loop equipment ？

loop The device is a pseudo disk , It USES image File as its storage backend . Linux dd The program provides a simple tool to create this image file .

practice

step 1： Check whether the root directory is larger than 10GB Remaining space of ,

[[email protected] ~]# df -h /
Filesystem           Size  Used Avail Use% Mounted on
/dev/mapper/rl-root   35G  1.9G   33G   6% /

step 2： Use dd Command to create a image file ,

[[email protected] ~]# dd if=/dev/zero of=/root/diskfile.img bs=1M count=8192
8192+0 records in
8192+0 records out
8589934592 bytes (8.6 GB, 8.0 GiB) copied, 13.7321 s, 626 MB/s
[[email protected] ~]# du -hs diskfile.img
8.0G    diskfile.img

step 3： Use losetup Tools , Will be image The file is set to loop equipment ,

[[email protected] ~]# losetup -fP diskfile.img
[[email protected] ~]# losetup -a # see 
/dev/loop0: [64768]:67202764 (/root/diskfile.img)

step 4： Partition .Linux There are several commands to complete disk partition , Use here fdisk,

[[email protected] ~]# fdisk /dev/loop0

Welcome to fdisk (util-linux 2.32.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Device does not contain a recognized partition table.
Created a new DOS disklabel with disk identifier 0x1f69de20.

Command (m for help): p
Disk /dev/loop0: 8 GiB, 8589934592 bytes, 16777216 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x1f69de20

Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-16777215, default 2048): 
Last sector, +sectors or +size{K,M,G,T,P} (2048-16777215, default 16777215): +2G

Created a new partition 1 of type 'Linux' and of size 2 GiB.

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

[[email protected] ~]# lsblk
NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
loop0         7:0    0    8G  0 loop 
└─loop0p1   259:0    0    2G  0 loop 
sr0          11:0    1 1024M  0 rom  
vda         252:0    0 40.1G  0 disk 
├─vda1      252:1    0    1G  0 part /boot
└─vda2      252:2    0 38.1G  0 part 
  ├─rl-root 253:0    0 34.2G  0 lvm  /
  └─rl-swap 253:1    0  3.9G  0 lvm  [SWAP]
vdb         252:16   0    5G  0 disk 

step 5： format partition

[[email protected] ~]# mkfs.xfs /dev/loop0p1
meta-data=/dev/loop0p1           isize=512    agcount=4, agsize=131072 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=1, sparse=1, rmapbt=0
         =                       reflink=1
data     =                       bsize=4096   blocks=524288, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0, ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
Discarding blocks...Done.

step 6： mount

[[email protected] ~]# mount /dev/loop0p1 /mnt
[[email protected] ~]# lsblk
NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
loop0         7:0    0    8G  0 loop 
└─loop0p1   259:0    0    2G  0 loop /mnt
sr0          11:0    1 1024M  0 rom  
vda         252:0    0 40.1G  0 disk 
├─vda1      252:1    0    1G  0 part /boot
└─vda2      252:2    0 38.1G  0 part 
  ├─rl-root 253:0    0 34.2G  0 lvm  /
  └─rl-swap 253:1    0  3.9G  0 lvm  [SWAP]
vdb         252:16   0    5G  0 disk 
[[email protected] ~]# mount | grep /mnt
/dev/loop0p1 on /mnt type xfs (rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota)
[[email protected] ~]# 

step 7： Use

[[email protected] ~]# echo "A test file." > /mnt/test.txt
[[email protected] ~]# cat /mnt/test.txt
A test file.
[[email protected] ~]# 

Reference material

https://man7.org/linux/man-pages/man4/loop.4.html#:~:text=The%20loop%20device%20is%20a,or%20to%20another%20block%20device.