I'm a newcomer to Ubuntu (due to the upcoming Windows 7 EOL) and I'm trying to test Ubuntu on a bootable USB stick, but I cannot get Steam to run because of a lack of space. How should I distribute the space on my USB so that Steam & a game can be tested?

I have used Rufus 3.8 to create a bootable USB stick containing Ubuntu 19.10 Eoan Ermine with a 16GB persistent partition.* I have been able to download the Steam installer. After installing, Steam downloaded 350MB of updates. Unfortunately, it has been unable to complete the update, saying that it needs 250MB more space. This appears to be correct, as Ubuntu's 'Files' utility say that the "casper-rw" partition only has 85 MB left.

The 'Disks' utility provides a different set of numbers. It says my 32GB** stick has a 14GB FAT Ubuntu partition (with 11GB free), a 17GB ext3 casper-rw partion, and 11GB free.

I am guessing that I need to make the persistent partition larger, but several points make me wonder whether I've done something else wrong. I am surprised that the Steam installer and runtime, without any games, have used up 16GB, because an installation is only supposed to require 5 GB. I am also puzzled that there is 11GB free in the Ubuntu partition: I thought that was supposed to be a read-only partition pretending to be a live CD, so there should not be any free (writable) space at all. Given that it's there, should I be trying to install Steam to somewhere other than the default location? Or should I try using Lubuntu or Xubuntu to make the OS smaller? Surely there's some way to squeeze Ubuntu and Steam onto a 32GB stick?!

*I know Steam says you should use 18.04LTS, but Rufus requires 19.10 for persistent USBs.

**Let's not quibble about GB or GiB here as it's probably irrelevant.


Solution with a persistent live USB pendrive and Ubuntu 18.04 LTS

This method should work for you because mkusb is designed to work with all current versions of Ubuntu.

  • If you have two USB pendrives, you can make a live-only system i Windows using Rufus with 18.04.1 or 18.04.3 LTS. This could be in a smaller and/or slower drive.

  • Boot into this live drive.

  • Install mkusb into it (live-only, but it will survive until its task is done and you reboot).
  • Create a persistent live drive in the other bigger and/or faster USB pendrive. mkusb will create a persistent live drive with a partition for persistence and you can select 100% of the available drive space for persistence.
  • Boot into the persistent live system
  • Install Steam and enjoy :-)


  • You can use an SSD in an external box and connect via USB 3 or eSATA. This will make a very fast system, almost like it were an internal drive.
  • You can create an installed Ubuntu system in a USB drive, pendrive or any other kind of external drive (e.g. SSD).
  • Thank you for taking time to help a stranger! Unfortunately, the main suggestion won't work and the alternatives are unworkable for me (though you couldn't know that from my post). Solution: There is an Ubuntu bug affecting all versions prior to 19.10. which means that you can't boot a live USB with a persistent partition. I tried installing 18.04.3 LTS just in case you had more up-to-date info, but it failed to boot in exactly the way the Rufus FAQ predicts ("mounting /cow on /root failed"). – Matthew Oct 20 '19 at 8:34
  • And anyway, the problem is not that Rufus limits the partition size; the issue was that I'm not clear what the optimal partition sizes are. I have now tried turning up the partition size to max. This does reduce the size of the Ubuntu partition but does not fix the Steam installation problem, unfortunately. I will post if I find a solution. Alternative A: I am using an old laptop that only has USB2, so SSDs are basically pointless. I am using a USB3 stick, as it's faster than my external HDDs. – Matthew Oct 20 '19 at 8:34
  • Alternative B: The linked answer for a full installation on USB says that you should physically disconnect the internal HDD before attempting this, and the Ubuntu wiki concurs. This is not a trivial task on a laptop. And it's a Lenovo with several proprietary hidden partitions, which is why I'm eager to test Ubuntu thoroughly before touching the internal HDD. If I trash the HDD, I just won't have any PC for at least a month.... :-( – Matthew Oct 20 '19 at 8:34
  • @Matthew, The two step procedure of my first alternative should work for you. First create a live-only USB drive with Rufus. Boot into it, install and use mkusb to create a persistent live system into another (best if fast USB 3 drive even in a USB 2 port). This method works with all current versions of Ubuntu. It is not affected by that bug. – sudodus Oct 20 '19 at 8:44
  • 1
    Note: A straightforward howto for mkusb/dus has just been added as an answer to a Superuser question. – Matthew Oct 21 '19 at 13:23


Another possibility is to create a Live USB with Rufus, UNetbootin or Universal, and add the word persistent to txt.cfg, (Rufus), or syslinux.cfg, (UNetbootin), and to grub.cfg for UEFI boot in either. Then format a second drive ext4 and label that partition casper-rw. This persistent partition can also be located on the computers HDD.

I prefer an installed system myself as described in Sudodus' link for long term flash drives, as they are more stable than a persistent drive and can utilize Nvidia graphic drivers, which is probably best for hard core gaming.

I understand that Sudodus is working on a solution to bad ext4 partitions created in Windows.


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