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Linux Horror Stories and Protection Spells (Volume I) (2021)

37 points by marcodiego 2y ago

Filligree 2y ago
You should, of course, have backups. And one form of backups which you should have are point-in-time snapshots; every ten minutes sounds good. I’ve lost count of the number of times I’ve deleted something I shouldn’t, but it’s never a big deal.
- blessedwhiskers 2y ago
  For those that run systems with zfs, sanoid makes this fairly trivial to configure on a per-dataset basis. It's saved me more than once. https://github.com/jimsalterjrs/sanoid https://github.com/jimsalterjrs/sanoid
pif 2y ago
[flagged]
- narayanbs 2y ago
  [flagged]
- ajford 2y ago
  Well that's reductive and dismissive. These are perfectly understandable mistakes or scenarios one might find themselves and a simple method to avoid/rectify them. Find is a very powerful and useful tool, and the author gave a clear example of when and where it might be useful. They also called out how to prevent accidents with `rm`.
- BazookaMusic 2y ago
  Hubris, followed by Nemesis when you accidentally delete that important config file that causes an outage. What if and backups are always a good idea when deleting via shell
- RamRodification 2y ago
  Would it make you feel better if it had the title "Linux Horror Stories and Protection Spells (from the perspective of a spoiled Windows user)"? Does it really matter?
  - keyringlight 2y ago
    As far as I can tell they didn't mention windows at all, unless this author is notorious for something I'm not aware of. The only places windows turns up on that blog seems to be for instructions that also apply to windows.
tester457 2y ago
Instead of `alias rm="rm –I"` for the confirmation dialog before removing a file, I prefer to use trash-cli[0] since I can restore trashed files. However, I haven't found a similar solution that works on Termux. [0] https://github.com/andreafrancia/trash-cli https://github.com/andreafrancia/trash-cli
- abnry 2y ago
  I do the same. My alias for rm just echos "use trash" so I don't replace its function, just disable it. When I really need to use rm I type /bin/rm.
  - 9dev 2y ago
    Bash also allows you to use \rm to override the alias. Comes in helpful at times.
- shagie 2y ago
  On a per directory basis... % touch -- -i % touch foo % touch bar % rm * zsh: sure you want to delete all 3 files in /Users/shagie/test [yn]? y remove bar? y remove foo? y % ls -i %
numberless 2y ago
This is from 2021¹, so it should probably have a (2021) ¹See bottom of article under who the author is
prmoustache 2y ago
Relying on aliases is the worse solution in my opinion. If it is protecting you too much, you will forget the risk and once for some reason you end up on a shell with a different profile you will forget about it and run a risky command.
- M95D 2y ago
  Exactly! I belive every user should make that kind of mistake at least once. That's how we become responsible users.
deleted 2y ago
[deleted]
deleted 2y ago
[deleted]
prewett 2y ago
Title is incorrect, I went for horror stories and all I got was unsolicited advice. Here's a couple classic horror stories for anyone like me: https://www.ecb.torontomu.ca/~elf/hack/recovery.html https://www.ecb.torontomu.ca/~elf/hack/recovery.html https://www.toddheberlein.com/blog/2014/4/16/how-rm-rf-almost-destroyed-pixar-and-a-pregnancy-saved-it https://www.toddheberlein.com/blog/2014/4/16/how-rm-rf-almos...
tetha 2y ago
Linux huge advantage: It gives you huge flexiblity and very sharp knifes. Linux drawback: Well, see above. It takes getting used to if. As I keep joking - nuking your first production system is a bit of a rite of passage as a linux admin. My first was a "mv $WORKSPACE/* $WORKSPACE/bin". I also once caused a ridiculous mess by screwing up NTP. It doesn't count 100% imo, but one of our juniors recently wanted to reset a DB on a newly installed system and did a "rm -rf /var /lib/foobar" to delete the system state. Another pretty green colleague wanted to cleanup a bunch of db dumps and ran "rm -rf /var/lib/barqux/*". It certainly removed the database dumps, and the database too. Both are now educated in the arts of either `find -delete`, `xargs -p`, as well as generating scripts full of individual `rm` or other calls for review. Some simple "for f in bla*; do echo 'mv $f ${f##blub#blob}' >> script; done" is a powerful technique. And I don't think they will forget this anytime soon, without anyone getting angry or anything. I'm mostly this chill about it because we have enough redundancy, automation and backups to let them run free and wild like this so they can learn quickly. Oh and yeah, they also learned how to reinit and/or rebuild database nodes, hah.
chasil 2y ago
For the "Too many files for a common directory" section, the xargs utility exists to address this problem. Modern (GNU) versions of xargs will also give you the ability to run operations in parallel: https://www.linuxjournal.com/content/parallel-shells-xargs-utilize-all-your-cpu-cores-unix-and-windows https://www.linuxjournal.com/content/parallel-shells-xargs-u... For the file removal problem, using a file system that supports (read-only) snapshots removes much of the pain. This can be done with zfs, btrfs, and the LVM subsystem can also do it with less advanced filesystems. I have never used the LVM snapshot features. https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/8/html/configuring_and_managing_logical_volumes/snapshot-of-logical-volumes_configuring-and-managing-logical-volumes#snapshot-of-logical-volumes_configuring-and-managing-logical-volumes https://docs.redhat.com/en/documentation/red_hat_enterprise_...
thefz 2y ago
> What makes find so powerful is that you can execute commands involving the found files using the option -exec. Or -print0 and pipe to xargs -0
- chasil 2y ago
  GNU find on rhel9 has explicit warnings about the -exec option: "There are unavoidable security problems surrounding use of the -exec action; you should use the -execdir option instead." "If you are using find in an environment where security is important (for example if you are using it to search directories that are writable by other users), you should read the `Security Considerations' chapter of the findutils documentation, which is called Finding Files and comes with findutils. That document also includes a lot more detail and discussion than this manual page, so you may find it a more useful source of information."

37 points by marcodiego 2y ago

You should, of course, have backups. And one form of backups which you should have are point-in-time snapshots; every ten minutes sounds good. I’ve lost count of the number of times I’ve deleted something I shouldn’t, but it’s never a big deal.

blessedwhiskers 2y ago
For those that run systems with zfs, sanoid makes this fairly trivial to configure on a per-dataset basis. It's saved me more than once. https://github.com/jimsalterjrs/sanoid https://github.com/jimsalterjrs/sanoid

pif 2y ago

[flagged]

narayanbs 2y ago
[flagged]
ajford 2y ago
Well that's reductive and dismissive. These are perfectly understandable mistakes or scenarios one might find themselves and a simple method to avoid/rectify them. Find is a very powerful and useful tool, and the author gave a clear example of when and where it might be useful. They also called out how to prevent accidents with `rm`.
BazookaMusic 2y ago
Hubris, followed by Nemesis when you accidentally delete that important config file that causes an outage. What if and backups are always a good idea when deleting via shell
RamRodification 2y ago
Would it make you feel better if it had the title "Linux Horror Stories and Protection Spells (from the perspective of a spoiled Windows user)"? Does it really matter?
- keyringlight 2y ago
  As far as I can tell they didn't mention windows at all, unless this author is notorious for something I'm not aware of. The only places windows turns up on that blog seems to be for instructions that also apply to windows.

tester457 2y ago

Instead of `alias rm="rm –I"` for the confirmation dialog before removing a file, I prefer to use trash-cli[0] since I can restore trashed files. However, I haven't found a similar solution that works on Termux. [0] https://github.com/andreafrancia/trash-cli https://github.com/andreafrancia/trash-cli

abnry 2y ago
I do the same. My alias for rm just echos "use trash" so I don't replace its function, just disable it. When I really need to use rm I type /bin/rm.
- 9dev 2y ago
  Bash also allows you to use \rm to override the alias. Comes in helpful at times.
shagie 2y ago
On a per directory basis... % touch -- -i % touch foo % touch bar % rm * zsh: sure you want to delete all 3 files in /Users/shagie/test [yn]? y remove bar? y remove foo? y % ls -i %

numberless 2y ago

This is from 2021¹, so it should probably have a (2021) ¹See bottom of article under who the author is

prmoustache 2y ago

Relying on aliases is the worse solution in my opinion. If it is protecting you too much, you will forget the risk and once for some reason you end up on a shell with a different profile you will forget about it and run a risky command.

M95D 2y ago
Exactly! I belive every user should make that kind of mistake at least once. That's how we become responsible users.

deleted 2y ago

[deleted]

deleted 2y ago

[deleted]

prewett 2y ago

Title is incorrect, I went for horror stories and all I got was unsolicited advice. Here's a couple classic horror stories for anyone like me: https://www.ecb.torontomu.ca/~elf/hack/recovery.html https://www.ecb.torontomu.ca/~elf/hack/recovery.html https://www.toddheberlein.com/blog/2014/4/16/how-rm-rf-almost-destroyed-pixar-and-a-pregnancy-saved-it https://www.toddheberlein.com/blog/2014/4/16/how-rm-rf-almos...

tetha 2y ago

Linux huge advantage: It gives you huge flexiblity and very sharp knifes. Linux drawback: Well, see above. It takes getting used to if. As I keep joking - nuking your first production system is a bit of a rite of passage as a linux admin. My first was a "mv $WORKSPACE/* $WORKSPACE/bin". I also once caused a ridiculous mess by screwing up NTP. It doesn't count 100% imo, but one of our juniors recently wanted to reset a DB on a newly installed system and did a "rm -rf /var /lib/foobar" to delete the system state. Another pretty green colleague wanted to cleanup a bunch of db dumps and ran "rm -rf /var/lib/barqux/*". It certainly removed the database dumps, and the database too. Both are now educated in the arts of either `find -delete`, `xargs -p`, as well as generating scripts full of individual `rm` or other calls for review. Some simple "for f in bla*; do echo 'mv $f ${f##blub#blob}' >> script; done" is a powerful technique. And I don't think they will forget this anytime soon, without anyone getting angry or anything. I'm mostly this chill about it because we have enough redundancy, automation and backups to let them run free and wild like this so they can learn quickly. Oh and yeah, they also learned how to reinit and/or rebuild database nodes, hah.

chasil 2y ago

For the "Too many files for a common directory" section, the xargs utility exists to address this problem. Modern (GNU) versions of xargs will also give you the ability to run operations in parallel: https://www.linuxjournal.com/content/parallel-shells-xargs-utilize-all-your-cpu-cores-unix-and-windows https://www.linuxjournal.com/content/parallel-shells-xargs-u... For the file removal problem, using a file system that supports (read-only) snapshots removes much of the pain. This can be done with zfs, btrfs, and the LVM subsystem can also do it with less advanced filesystems. I have never used the LVM snapshot features. https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/8/html/configuring_and_managing_logical_volumes/snapshot-of-logical-volumes_configuring-and-managing-logical-volumes#snapshot-of-logical-volumes_configuring-and-managing-logical-volumes https://docs.redhat.com/en/documentation/red_hat_enterprise_...

thefz 2y ago

> What makes find so powerful is that you can execute commands involving the found files using the option -exec. Or -print0 and pipe to xargs -0

chasil 2y ago
GNU find on rhel9 has explicit warnings about the -exec option: "There are unavoidable security problems surrounding use of the -exec action; you should use the -execdir option instead." "If you are using find in an environment where security is important (for example if you are using it to search directories that are writable by other users), you should read the `Security Considerations' chapter of the findutils documentation, which is called Finding Files and comes with findutils. That document also includes a lot more detail and discussion than this manual page, so you may find it a more useful source of information."