Resize /dev/root on CentOS 7.4 [duplicate]

Question

I'd like to give /dev/root more space on my CentOS 7.4 system.

# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/root        20G   18G  302M  99% /
devtmpfs        7.8G     0  7.8G   0% /dev
tmpfs           7.8G   28K  7.8G   1% /dev/shm
tmpfs           7.8G  826M  7.0G  11% /run
tmpfs           7.8G     0  7.8G   0% /sys/fs/cgroup
/dev/sda2       1.8T  2.7G  1.7T   1% /home
tmpfs           1.6G     0  1.6G   0% /run/user/0

As you can see I have more than enough space mounted to /home.

# /sbin/fdisk -l
Disk /dev/sda: 2000.4 GB, 2000398934016 bytes, 3907029168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk label type: dos
Disk identifier: 0xf2e91416

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        4096    40962047    20478976   83  Linux
/dev/sda2        40962048  3905974271  1932506112   83  Linux
/dev/sda3      3905974272  3907020799      523264   82  Linux swap / Solaris

How can I add 500 GB to /dev/root ?

Is this possible without going into rescue mode?

If not which commands do I need to do it in a Debian based rescue environment?

Edit: Ended up reinstalling with better partitioning.

Answer 1

I can't see any easy way to do this. I don't know how you finished up with / in your boot partition: normally this is mounted as /boot/efi (or it is on Ubuntu at least).

What I would do is:-

• Back up the whole disc /dev/sda (you'll need to do this anyway), then re-install from scratch, hoping to get the partition structure correct this time.
• Then from a Live Boot disc mount /dev/sda2 (which is where / should be), maybe at /mnt/newsys, as well as the back-up of /dev/sda1 (/dev/sdb1, perhaps?), maybe at /mnt/oldsys.
• Now run cp -ua /mnt/oldsys/ /mnt/newsys/.
• Next mount the back-up of /dev/sda2, perhaps at /mnt/oldhome.
• Lastly run cp -ua /mnt/oldhome/ /mnt/newsys/home/.

There may be ways to avoid regenerating, but you will probably spend more time trying to avoid it than you would doing it.