Bootable Linux USB stick
We regularly and successfully use USB sticks for courses where participants bring their own notebooks. The big benefit is that students learn Linux, and realize that they can easily use the hardware they already own. Current notebook hardware is by far fast enough for data processing, structure solution and coot visualization. What we found:
- the sticks should be fast USB3 (very good results with SANdisk Extreme 32GB). The computers do_not_ have to be recent, nor do they have to have USB3 ports
- we use Fedora 23 because its hardware support is very good
- we produce >50% BIOS-bootable sticks and the rest are EFI-bootable sticks (we have not yet found out how to combine this into one). The latter can be booted on Macbooks as well; their hardware works well with Fedora 23. For Windows clients, one has to make sure that "fast boot" (or "fast startup") is disabled (or Shift is pressed while shutting Windows down), and sometimes powercfg -H off (as Administrator in a console window) is additionally required; otherwise the USB stick may not boot. Occasionally we find a computer that does not boot from any of the sticks because the BIOS screen can not be reached (due to unknown BIOS password; happens with machines belonging to institutions which administer them centrally) or some such, but 19 out of 20 work as they should.
- performance tuning (not required): We use an ext4 filesystem and
data=writeback,nobarrierin /etc/fstab. To set the writeback option on the / filesystem one needs to use tune2fs on a Linux machine where the stick is just mounted (i.e. not booted from), with the option data_journal_writeback; one should also set nobarrier that way. With this tuning the stick is as fast as a local harddisk.
- we always create a few-GB FAT32 partition because that makes file exchange with Windows and Macs very simple
- we just install CCP4 and whatever else we need (XDS, Phenix, Chimera, ..), and then dd or ddrescue (on a machine with USB3 ports) an image of that stick to all other sticks.
- any number of bells and whistles could be added to this, like clients sending their hostnames to a server after booting, and accepting updates by rsync.
To make students familiar with the sticks and how to boot them, one needs 30+ minutes and a few tutors.
If somebody figures out how to install Fedora23 sticks that boot on both BIOS- and EFI hardware, I'd like to hear about this.
Some more details
- As for normal OS installation it matters if for the installation of the stick your computer is booted in BIOS mode (on newer machines "CSM enabled") --> you obtain a stick which boots BIOS systems, or if for the installation your computer is booted in EFI mode --> you obtain a stick which boots in EFI mode on newer computers and Macs
- the SANdisk Extreme is the best stick we found; physically small sticks look nicer but are slow (even though they are called USB3)
- we always use the 64bit distro
- the FAT32 partition should be the first partition on the stick; 2GB is enough for us. Then comes the Linux partition, with 13.9GB, so that the sum of the two partitions is slightly below 16GB. The third partition is then a 16.1GB /data partition. This scheme has the advantage that the image of the stick can just as well be copied (with dd or better ddrescue) to a 16GB stick; the /data partition then does not fit and cannot be used on that stick, but the operating system will then work on the small stick just as well. This requires that the /data partition is not mounted automatically from /etc/fstab (i.e. it should be listed, but with the noauto option), but rather with a command like "mount /data &" from /etc/rc.local - because if the 16GB stick is booted, it will otherwise find a corrupt filesystem and the boot will fail, leaving you with a rudimentary shell prompt which only experts can recover from. Also this means that the image of the stick need only comprise the first 16GB (unless the /data partition already has something on it) - that makes it faster to copy it, and it is quite fast to re-create an empty /data partition after booting the stick.
- it is a good idea to give easy root access to the one user you create because certainly some packages will have to be installed or updated when the stick is in use
- it is a good idea to save an image of the stick whenever you made a successful change; otherwise you might need to start from scratch if you mess something up.
- (if the installation not already does it for you) you should label the partitions and use the labels for mounting the partitions in /etc/fstab; don't use /dev/sda1 or the like because depending on the hardware it is booted on, after booting the stick, and depending on the actual hardware, the stick may be /dev/sdb or /dev/sdc !