this post was submitted on 21 Aug 2024

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What is the most duct-tape thing you've done to Linux? (lemm.ee)

submitted 3 weeks ago* (last edited 3 weeks ago) by [email protected] to c/[email protected]

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tell me the most ass over backward shit you do to keep your system chugging?
here's mine:
sway struggles with my dual monitors, when my screen powers off and back on it causes sway to crash.
system service 'switch-to-tty1.service'

[Unit]
Description=Switch to tty1 on resume
After=suspend.target

[Service]
Type=simple
ExecStart=/usr/local/bin/switch-to-tty1.sh

[Install]
WantedBy=suspend.target

'switch-to-tty1.service' executes '/usr/local/bin/switch-to-tty1.sh' and send user to tty1

#!/bin/bash
# Switch to tty1
chvt 1

.bashrc login from tty1 then kicks user to tty2 and logs out tty1.

if [[ "$(tty)" == "/dev/tty1" ]]; then
    chvt 2
    logout
fi

also tty2 is blocked from keyboard inputs (Alt+Ctrl+F2) so its a somewhat secure lock-screen which on sway lock-screen aren't great.

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[–] [email protected] 14 points 3 weeks ago (2 children)

Mounting a Samba share and moving my LVM pvolumes of / onto a losetup'ed file on it, while running the system. Bass ackwards.

[–] [email protected] 7 points 3 weeks ago (1 children)

Good grief. Why?

[–] [email protected] 5 points 3 weeks ago (1 children)

I needed to redo partitions, but didn't want to reboot.

[–] [email protected] 3 points 3 weeks ago (1 children)

That's not even a bad idea then.

One of my machines has a boot partition that's a bit too small, on an otherwise LVM setup.

[–] [email protected] 4 points 3 weeks ago (1 children)

I'd recommend a Linux installer on a memory stick, instead. It's bound to have less network lag.

[–] [email protected] 3 points 3 weeks ago (1 children)

Nah, it'll be fine.

I might have a large enough USB SSD laying around some where. I could probably use that instead.

extend VG with the USB PV
move LV's to USB
shrink root LV
resize boot
move things back on a new internal PV

[–] [email protected] 2 points 3 weeks ago (1 children)

Does your FS support online resizing? EXT4 doesn't, so you'd have to use an installer stick.

Be super careful about partition sizes. I once tried to shrink my FS to an exact size, then shrink the LV to the same size - it ended up corrupting my FS. After that time, I started undersizing the FS, then resizing LV, finally expanding the FS again.

Have backups.

[–] [email protected] 1 points 3 weeks ago (1 children)

Does your FS support online resizing?

Yeah. I mainly use btrfs; it supports online growing and shrinking.

Be super careful about partition sizes. [...]

I know. I have done plenty of same device partition resizing. I know the pit falls, and for safety shrink the FS to below what the LV is going to be.

Have backups.

Thanks for the reminder. I've been meaning to set up snapshot backups for this machine using rsnapshot as an experiment. I mainly use Dirvish

[–] [email protected] 2 points 3 weeks ago (1 children)

I use rsync with a custom shell script to manage the number of incremental copies. You'll probably prefer something less janky.

[–] [email protected] 1 points 3 weeks ago

That sounds pretty much like what Dirvish and rsnapshot do. Both wrap rsync.

[–] [email protected] 1 points 3 weeks ago (1 children)

Did it work? There's a huge chance of data corruption if you are copying the disk of a running system.

[–] [email protected] 1 points 3 weeks ago

It didn't, but due to unrelated reasons. The root FS was mounted r/w, so the regular IO eventually overwhelmed the network's ability to copy stuff.

But no worries, a reboot later, with unmounted FS, I finished the same thing.

Copying the disk of a running system appears to be fine in LVM. Copying is done block-by-block, and the only thing it has to do to make it atomic is: in case of a conflict (writing into a block that's being copied right now), postpone writing to a block until it's copied, then finish the write in the new location. Or else, abort the copy, finish the write, then copy again.