fgaz
I somehow managed to accidentally delete /dev/null and it’s unbelievable how much stuff relies on writing data to nothing.
your new favourite fungus
Haelwenn /элвэн/ :triskell:
fgaz
The answer appears to be 0. They just like to know that it’s there
fgaz
Just how much data gets produced and the immediately thrown away into /dev/null at any given moment?
Hmm actually I can easily find that out…
fgaz
Like… I know it’s required by POSIX, and it’s helpful in scripts, but how is it possible that standalone programs rely on it instead of just… not producing that data.
Just how much data gets produced and the immediately thrown away into /dev/null at any given moment?
fgaz
But wait, that was a regular file! A file that can be overwritten (and reset to 0 bytes) by multiple processes, so it could be that I just didn’t see the data in time.
So I tried to make it a FIFO… forgetting that FIFOs are blocking until a reader is set up. My shell instantly locked up, and so did the most random parts of the system
Haelwenn /элвэн/ :triskell:
Attie Grande
@lanodan @fgaz @duponin if by "regular file" you mean "character special", then sure... and what about sysfs, securityfs, debugfs, etc... for pseudo-filesystems?
"Virtual File System", or VFS is different again?
https://docs.kernel.org/filesystems/vfs.html
Attie Grande
@lanodan ah, thought I was having a moment there 😂🙈
Haelwenn /элвэн/ :triskell:
a kilo of saucepans (rakslice)
@lanodan @fgaz @duponin that's not what "regular file" means on Linux (or any Unix)
a kilo of saucepans (rakslice)
@lanodan just like "we all know" nobody was asking how it's possible to delete /dev/null
Haelwenn /элвэн/ :triskell:
Jordan :ms_nonbinary_flag:
@fgaz At a job long in the past, I had a coworker who was very enamored of a particular do-everything Python library which I will not name at this time. This library included some built-in logging facilities, but he didn't actually need the log for the thing he was making, so he set it to log to `/dev/null`.
It turns out that this library had automatic log rotation built in. The way it worked was that it kept track of the number of bytes written to a log, and when it crossed a certain threshold, it would rename the file it was logging to, and open a new log file.
Unfortunately, the thing my coworker built ran as `root`. It started up and ran fine for a while, merrily logging to `/dev/null` as instructed. After a while, though, it noticed "oh hey I've written more than a megabyte of logs, time to rotate the log file" - it then renamed `/dev/null` to `/dev/null.YYYY-mm-dd.HH:MM:SS` and created a new `/dev/null` that was just a regular text file. From that point onward, anything that got written to `/dev/null` actually got written to disk. Chaos ensued.
That one took a whole day to figure out...
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