Resize a Linux Root Partition Without Rebooting
Introduction
Its a very common occurance that i may need to increase the disk size on a VM. In the following example we have a disk that is divided into two partitions. The first one, /dev/vda1, is the boot partition where the OS resides. The second partition, /dev/vda2, is configured as swap space.
root@debian:~# fdisk -l /dev/vda
Disk /dev/vda: 50 GiB, 53687091200 bytes, 104857600 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: 0x0041f8a8
Device Boot Start End Sectors Size Id Type
/dev/vda1 2048 96471039 96468992 46G 83 Linux
/dev/vda2 96471040 104857599 8386560 4G 82 Linux swap / Solaris
In the example above, the total 50 GB storage volume is split into 46 GB usable space and 4 GB for swap. What if after provisioning we find that 46 GB of disk space is not enough but we prefer not to add an additional storage volume? The goal is to increase the amount of disk space available on the root filesystem. This can be accomplished with minimal disruption. We do not need to reboot the server!
We then need to switch off the swap - so make sure you can live a few minutes without swap space:
root@debian:~# swapoff -a
Once swap has been disabled, we need to reconfigure the partitions using fdisk:
We will delete the two existing partitions first. We run fdisk /dev/vda and then use the d command to delete partition 2, and then delete partition 1. Follow the example below:
root@debian:~# fdisk /dev/vda
Command (m for help): d
Partition number (1,2, default 2):
Partition 2 has been deleted.
Command (m for help): d
Selected partition 1
Partition 1 has been deleted.
Now we recreate our partitions. In the example we have 4 GB of swap space. So we need to keep at least that much space available for the new swap partition.
Recreate /dev/vda1 first. Press n to create a new partition. Enter p to create a primary partition. We can press Enter to accept the default value of 2048 for the first sector. Then enter a size for the partition. You can enter a value in GB, so if we are increasing the disk to 100 GB, we subtract our 4 GB for swap, and enter +96G for 96 GB.
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 (2048-209715199, default 2048):
Last sector, +sectors or +size{K,M,G,T,P} (2048-209715199, default 209715199): +96G
Created a new partition 1 of type 'Linux' and of size 96 GiB.
Now we recreate the swap partition following a simalar process. Press n and then p to create a new primary partition. Press Enter to accept the default value for "First sector". We can also press Enter again to accept the default value for "Last sector".
Command (m for help): n
Partition type
p primary (1 primary, 0 extended, 3 free)
e extended (container for logical partitions)
Select (default p): p
Partition number (2-4, default 2): 2
First sector (201328640-209715199, default 201328640):
Last sector, +sectors or +size{K,M,G,T,P} (201328640-209715199, default 209715199):
Created a new partition 2 of type 'Linux' and of size 4 GiB.
Since this second partition is going to be used for swap space, we need to change the partition type. This can be done by pressing t at the fdisk prompt. We then press 2 to select the second partition. If you want to see the list of available partition types, press L, otherwise enter 82 to select "Linux swap / Solaris".
Command (m for help): t
Partition number (1,2, default 2): 2
Partition type (type L to list all types): L
0 Empty 24 NEC DOS 81 Minix / old Lin bf Solaris
1 FAT12 27 Hidden NTFS Win 82 Linux swap / So c1 DRDOS/sec (FAT-
2 XENIX root 39 Plan 9 83 Linux c4 DRDOS/sec (FAT-
3 XENIX usr 3c PartitionMagic 84 OS/2 hidden or c6 DRDOS/sec (FAT-
4 FAT16 <32M 40 Venix 80286 85 Linux extended c7 Syrinx
5 Extended 41 PPC PReP Boot 86 NTFS volume set da Non-FS data
6 FAT16 42 SFS 87 NTFS volume set db CP/M / CTOS / .
7 HPFS/NTFS/exFAT 4d QNX4.x 88 Linux plaintext de Dell Utility
8 AIX 4e QNX4.x 2nd part 8e Linux LVM df BootIt
9 AIX bootable 4f QNX4.x 3rd part 93 Amoeba e1 DOS access
a OS/2 Boot Manag 50 OnTrack DM 94 Amoeba BBT e3 DOS R/O
b W95 FAT32 51 OnTrack DM6 Aux 9f BSD/OS e4 SpeedStor
c W95 FAT32 (LBA) 52 CP/M a0 IBM Thinkpad hi ea Rufus alignment
e W95 FAT16 (LBA) 53 OnTrack DM6 Aux a5 FreeBSD eb BeOS fs
f W95 Ext'd (LBA) 54 OnTrackDM6 a6 OpenBSD ee GPT
10 OPUS 55 EZ-Drive a7 NeXTSTEP ef EFI (FAT-12/16/
11 Hidden FAT12 56 Golden Bow a8 Darwin UFS f0 Linux/PA-RISC b
12 Compaq diagnost 5c Priam Edisk a9 NetBSD f1 SpeedStor
14 Hidden FAT16 <3 61 SpeedStor ab Darwin boot f4 SpeedStor
16 Hidden FAT16 63 GNU HURD or Sys af HFS / HFS+ f2 DOS secondary
17 Hidden HPFS/NTF 64 Novell Netware b7 BSDI fs fb VMware VMFS
18 AST SmartSleep 65 Novell Netware b8 BSDI swap fc VMware VMKCORE
1b Hidden W95 FAT3 70 DiskSecure Mult bb Boot Wizard hid fd Linux raid auto
1c Hidden W95 FAT3 75 PC/IX bc Acronis FAT32 L fe LANstep
1e Hidden W95 FAT1 80 Old Minix be Solaris boot ff BBT
Partition type (type L to list all types): 82
fdisk helpfully informs us that we have changed the partition type with the message:
Changed type of partition 'Linux' to 'Linux swap / Solaris'.
After that, we save using the w command and are returned to a shell prompt:
Command (m for help): w
You may get a message like this before the shell prompt:
The partition table has been altered.
Calling ioctl() to re-read partition table.
Re-reading the partition table failed.: Device or resource busy
The kernel still uses the old table. The new table will be used at the next reboot or after you run partprobe(8) or kpartx(8).
Lets forgo rebooting and instead tell the kernel about the new partitions using partprobe:
root@debian:~# partprobe
If you get a command not found it may be helpfull to install the parted package
apt-get install parted
``
We should be returned to the shell prompt with no output from partprobe.
Now we need to resize our filesystem on /dev/vda1:
root@debian:~# resize2fs /dev/vda1
resize2fs 1.42.12 (29-Aug-2014)
Filesystem at /dev/vda1 is mounted on /; on-line resizing required
old_desc_blocks = 2, new_desc_blocks = 3
The filesystem on /dev/vda1 is now 25165824 (4k) blocks long.
Initialize the new swap location of /dev/vda2:
root@debian:~# mkswap /dev/vda2
Setting up swapspace version 1, size = 4193276 KiB
no label, UUID=c55c25a2-a386-4653-8455-4d9030586dd2
Finally we edit /etc/fstab and replace the old UUID with the new one returned in the output of the mkswap command. The line to change has no value for "mount point" and has "type" set to swap.
#/etc/fstab: static file system information.
#Use 'blkid' to print the universally unique identifier for a
#device; this may be used with UUID= as a more robust way to name devices
#that works even if disks are added and removed. See fstab(5).
#<file system> <mount point> <type> <options> <dump> <pass>
UUID=332f8fb5-ff1f-4297-b512-f2c93a277296 / ext4 errors=remount-ro 0 1
/dev/fd0 /media/floppy0 auto rw,user,noauto,exec,utf8 0 0
UUID=c55c25a2-a386-4653-8455-4d9030586dd2 none swap sw 0 0
After editing /etc/fstab, we need to enable swap again:
root@debian:~# swapon -a
Verify
We can verify the new larger disk size by utilizing df and/or fdisk.
Device Boot Start End Sectors Size Id Type
/dev/vda1 2048 201328639 201326592 96G 83 Linux
/dev/vda2 201328640 209715199 8386560 4G 82 Linux swap / Solaris
We can also confirm that the server was not rebooted by looking at the output of uptime:
$ uptime
23:54:21 up 7 days, 1:15, 1 user, load average: 0.00, 0.01, 0.05
Summary
We have successfully increased the amount of disk space available on our Linux server.