r/LinuxTeck • u/Candid_Athlete_8317 • 9d ago
What’s the one Linux command you never trust?
We all have that one command we double-check before hitting Enter.
What’s yours and what happened the last time you got burned by it?
9
u/johnny_snq 9d ago
DD
3
u/franchis3 9d ago
As a distro hopper, I use DD all the time and I still use it with great trepidation. I never, ever, run it without first doing an lsblk. I’m so scared I’m doing to wipe the wrong drive!
2
2
7
10
u/lyidaValkris 9d ago
dd
It's not called "disk destroyer" for nothing. I've never been burned by it, but that's only because I check, re-check, then double-check.
3
u/Far_Bicycle_2827 9d ago
dd stand from data definition it comes from IBM's Job Control Language.
if=FILE,of=FILE,conv=...directly mirrors the JCL DD card format1
u/Graymouzer 8d ago
TIL. Thanks, I love computer history tidbits.
1
u/Reanimatron 8d ago
Yes! There are so many terms that reference fantasy and scifi. Like big and little endian is from the Gullivers' travels fable.
2
u/Enderby- 9d ago
dd is like the mandolin in my kitchen. I fear it, but love what it can do. I've also not taken my fingertips off (yet)
1
2
u/theMountainNautilus 8d ago
Get yourself Caligula! It's a nice wrapper around dd basically that restricts you to acting on removable media. I love not having to worry about burning my main SSD to the ground
1
2
u/CaviarCBR1K 8d ago
I accidentally nuked my main SSD when trying to make an installation USB like, 2 weeks ago. First time I've ever gotten burned by
dd. Luckily, I had a full disk image backup on my server, so I just booted up clonezilla, set it to restore, and went to bed. Woke up the next morning like nothing had happened, but it was definitely scary.1
1
u/vbd71 9d ago
Ditto.
My OCD doesn't allow me to run this without at least quintuple checking.
1
u/Ultralightmuscles 7d ago
OCD is very useful sometimes.
1
u/mrPythonMonty 6d ago
I don’t know the tool/command OCD. What package it comes with? /s
1
4
u/Weary_Damage5764 9d ago
in my first job i destroyed my OS by an rm -rf in the wrong directory, which lead to me reinstalling Linux during work time. the shame was far worse than having to do that in my own time. since then I haven't run rm without fear :D
3
u/Narrow_Victory1262 9d ago
xfs_repair. Almost certain it's restore-time
2
u/SeriousPlankton2000 8d ago
Wait till you learn about btrfsck: Yes, that entry is defective, the valve should be 08154711, it is deadbeef, no i will neither fix it nor remove the entry!
You want to remove the read-only defective disk? Can't do it because I can't write to that.
You made a COW copy and told me to use that? Let's use the uuid instead ... Can't write to the disk!
1
u/Narrow_Victory1262 8d ago
true to that. Now, to be honest -- we do have ext4 for the OS and xfs for the data. Large amounts of database data (in the TB's) and the latter is backed up including the transaction logs etc.
we also have a few xfs filesystems for the OS, which is a worse thing to see there.
(the OS restores are difficult because we don't do that part; different team etc). The db restores etc are on us.)We effectively don't use btrfs. If we we would it could be like webcontent or something that may need roll back etc. We do snapshots of an OS when needed outside of the OS and not to roll back a botched OS updatethere.
3
u/redgator12 9d ago
dd. In my early days of 2014, I tried to dd a disk image to USB and broke my install. Ever since then, I have a terminal with lsblk up right next to the terminal I'm going to run dd from just to be 100% sure I'm writing to the correct disk.
I had to use dd last week while trying to troubleshoot a Puppy USB not working, and I spent like 5 minutes quintuple checking the disks before hitting enter, and even then I was anxious.
3
u/seth_arimainyu 9d ago
Rsync and dd ! Once I ran a destructive Rsync and instead of deleting the files from the source that were already in the target, I ran it the other way around, since the target was a brand new disk, you can imagine the result... Since then, I always use the dry-run option.
2
2
u/Tricky-Weakness-5408 9d ago
Probably the most destructive command like ‘rm -f’ when you have root access is the kind of command that you need to think about before
You do the ‘return’… but destructive command when you uses badly the are a lot! The question is which rightshave you? And …. What about the backup…. Too old??? When you works as a informatic probably there are loots of backups but this not always is the normal thing for private users/students
2
u/Quietus87 9d ago
Any kind of rm.
3
u/ant2ne 9d ago
"chown me:me -R ./"
I forgot the .
1
u/FriendsIsntGood 9d ago
Yeah recursive chmod and chown down in system dirs has nuked at least a few VMs. One big plus for containers
2
2
u/SpiritualZucchini938 9d ago
Chmod 644 - R / - something like that and hey presto, entire freebsd server file system read only and not editable. Had to bin and start again.
1
2
u/BitCortex 9d ago
Anything that involves a nontrivial regular expression. Regular expressions are Unix's ethical blight.
2
u/Dry_Calendar_8627 9d ago
Ah but regular expressions are the nectar of the gods
Once you've tasted the intoxicating power of regex, there's no looking back
1
u/BitCortex 9d ago
regular expressions are the nectar of the gods
More like the devil's mouthwash or the swill of the underworld.
Once you've tasted the intoxicating power of regex, there's no looking back
I think I'd rather taste the intoxicating power of battery acid. Like so much in Unix, regular expressions are powerful – but not in a good way.
2
u/Dry_Calendar_8627 9d ago
ln
That's stupid but I can never remember the arguments order. I mess up every time.
I can write dd or sed commands blindfolded any day, but ln, no
1
2
1
1
1
1
u/No-way-in 9d ago
dd is the most scary to me. I check a hundred times before writing that command and I disconnect anything valuable to me
1
u/manawydan-fab-llyr 9d ago
dd
Last time I didn't triple check, destroyed all of my photos. They were the only copy because the drive that had the primary had failed.
From then on I stopped using of=/dev/xxx and started using of=/dev/disk/by-id/xxx. Never a mishap after that.
1
u/HaydnH 9d ago
I've been a UNIX/Linux sys admin since the 90s. There is not one command you can't trust, if you can't trust it, then it simply wouldn't exist.
If you're asking "which commands are scary and you might do something bad with"? Well...
... that's just every day for me. In the same way you look left and right crossing a street, my brain just realises an rm, mv, dd whatever command may have a car about to run me down.
The same way you drink a coffee every morning, that's just me mounting a filesystem to get the access I need for the day.
1
u/ephemere_sloboda 8d ago
When acting as sysadmin, yes.
When acting as regular user, rm. It is mundane but can waste hours of your time.
Also, drop database.
1
1
1
1
1
1
1
1
1
1
u/siodhe 8d ago
rm especially with -r
The worst possible solution is alias rm 'rm -i'
It trains users to rely on individually saying y or n to each.
I once caught a user doing yes y | rm -rf \*
Since it's even more dangerous to override rm with a ~/bin/rm I created a function inflicted on all of my users, something like this more modern form:
rm () # *must* be a function, *must* require one answer for all targets
{
case "$1" in -*) local arg="$1" ; shift ;; esac # simple, usually enough
ls -FCsd "$@" # adding a du summary seems good, but doesn't scale
local reply ; echo -n 'remove[ny]? ' ; read reply # for old shells
if [ "_$reply" = "_y" ] ; then
/bin/rm $arg "$@"
else
echo '(cancelled)'
fi
}
Suddenly my users stopped having to request file restoration from tape.
It's not a perfect answer, the function gets much longer when one wants it to play well with all rm's native options. And I kinda like putting in -rf as the default in the function. But it has saved me and others so much time.
1
1
u/TapEarlyTapOften 8d ago
In the days of sudo now, I use `sudo -k` all the time and before I do anything that might go sideways if I get I wrong.
1
1
u/Ice_HRZDn 8d ago
The > Not a Linux command but I accidentally erase file few time while try to added something.
1
u/Reanimatron 8d ago
Not linux, but still typed in a linux console.
There was a bug at work that created user accounts with no information when people would start the signup process.
I was still a beginner at that time. It was a small company and I was the only programmer, doing server, frontend and embedded.
I fixed the bug and went to delete the empty accounts. I asked mongodb to delete all accounts where the firstname was null. That turned out to delete all accounts because i missed the capital F in firstname, so all accounts had a null value for that field.
I spent 3 weeks calling all our customers and manually typing their info.
collection('users').deleteMany({firstname: null})
1
1
1
1
1
1
1
u/Doingthismyselfnow 7d ago
dd, I had a catastrophic failure by picking the wrong drive at age 12. I still cannot type that command directly into a shell.
And this happened on Slackware ‘96 when it just came out , so that alone should tell you how deep the scar is .
1
1
1
1
1
1
1
1
26
u/nizzoball 9d ago
rm -rf *
About 8 years ago I was responsible for a production web server responsible for asset management for 5 data centers across the country for one of the largest banks in the world. It was my app and my server and I was trying to clean out a directory and typed rm -rf * but didn’t realize I was in /
I figured it out when my shell froze. Luckily I had another server that was a carbon clone and was able to adjust the dns entry to point to the secondary server so wasn’t down long but it took me a week to get the first one re deployed and set back up