Partitioning – How to Resize Partitions Using Command Line Without GUI on a Server

command linepartitioningswap

I only have access to the server via a terminal and I can't use graphical tools such as GParted!
I want to create a new partition from a part of the root (about 768mb) for swap.

# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/vda         20G  1.3G   18G   7% /
udev             10M     0   10M   0% /dev
tmpfs           199M  4.9M  194M   3% /run
tmpfs           100M   12K  100M   1% /run/user
tmpfs           5.0M  4.0K  5.0M   1% /run/lock

Best Answer

You cannot shrink/edit a partition if any of the partition on the storage device is mounted. So in order to unmount and edit the root filesystem, the OS need to be shutdown. Then boot into a live system and edit the partition as described in other answers.

Alternative solution : swap file

As an alternative to creating an entire partition, a swap file offers the ability to vary its size on-the-fly, and is more easily removed altogether. Swap file can be hot plugable. i.e can be added and removed without unmounting/turning off the OS.

  1. Create a 512 MB file called /swapfile. This will be our swap file. 

    fallocate -l 512M /swapfile

    OR 

    dd if=/dev/zero of=/swapfile bs=1M count=512

  2. Set the right permissions (because a world-readable swap file is a huge local vulnerability): 

    chmod 600 /swapfile

  3. After creating the correctly sized file, format it to swap: 

    mkswap /swapfile

  4. Activate the swap file: 

    swapon /swapfile

  5. Edit /etc/fstab and add an entry for the swap file: 

    /swapfile none swap defaults 0 0

More details at arch linux wiki.

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