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Modern Versions of systemd Can Cause an Unmount Storm During Shutdowns

posted by Fnord666 on Sunday May 10 2020, @06:47PM   Printer-friendly
from the stormy-weather dept.

canopic jug writes:

System adminsitrator Chris Siebenmann has found Modern versions of systemd can cause an unmount storm during shutdowns:

One of my discoveries about Ubuntu 20.04 is that my test machine can trigger the kernel's out of memory killing during shutdown. My test virtual machine has 4 GB of RAM and 1 GB of swap, but it also has 347 NFS[*] mounts, and after some investigation, what appears to be happening is that in the 20.04 version of systemd (systemd 245 plus whatever changes Ubuntu has made), systemd now seems to try to run umount for all of those filesystems all at once (which also starts a umount.nfs process for each one). On 20.04, this is apparently enough to OOM[**] my test machine.

[...] Unfortunately, so far I haven't found a way to control this in systemd. There appears to be no way to set limits on how many unmounts systemd will try to do at once (or in general how many units it will try to stop at once, even if that requires running programs). Nor can we readily modify the mount units, because all of our NFS mounts are done through shell scripts by directly calling mount; they don't exist in /etc/fstab or as actual .mount units.

[*] NFS: Network File System
[**] OOM Out of memory.

We've been here before and there is certainly more where that came from.

Previously:
(2020) Linux Home Directory Management is About to Undergo Major Change
(2019) System Down: A systemd-journald Exploit
(2017) Savaged by Systemd
(2017) Linux systemd Gives Root Privileges to Invalid Usernames
(2016) Systemd Crashing Bug
(2015) tmux Coders Asked to Add Special Code for systemd
(2016) SystemD Mounts EFI pseudo-fs RW, Facilitates Permanently Bricking Laptops, Closes Bug Invalid
(2015) A Technical Critique of Systemd
(2014) Devuan Developers Can Be Reached Via vua@debianfork.org
(2014) Systemd-resolved Subject to Cache Poisoning

Original Submission

 
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  • (Score: 0) by Anonymous Coward on Monday May 11 2020, @09:02PM

    by Anonymous Coward on Monday May 11 2020, @09:02PM (#993073)

    Shell script is anathema for systemd. Any admin can debug that with a plain editor, or even test interactively by copy & paste, then edit lines in shell history (basic REPL). Not in the systemd vision.

    We already concluded that IBM (and RH before them) plan is to add complexity so only them can touch the steering wheel, and all the rest have to buy support contracts and training, and "enjoy" the ride. And as you said in the past, other projects bent over dreaming they will still matter in the future and everything will be roses by then, when Rome does not pay traitors (that is the part I add).

    Free Software licenses like GPL require distribution of "source code needed to generate, install, and (for an executable work) run the object code and to modify the work, including scripts to control those activities". Corporations found the loophole, the license does not say anything about making such big mess that people can make use of their freedoms. The mess is so big in some projects, that even small companies can not do it. Even less so, fork a project to try to get it back into sanity.