ulimit confusion.

WarrenUK

Hi.

I've been playing around with ulimit and I have some questions.

If I raise a limit with $ ulimit -n 10000 is this hard or soft?

If I raise a limit with $ ulimit -n 1025 it works, then I try to lower the limit back to its default 1024 with $ ulimit -n 1024 I get an error. Why?

To edit the /etc/security.limits.conf is it safe to use vim/nano?

Thanks.

luisviveropena

Hi @WarrenUK ,

If I raise a limit with $ ulimit -n 10000 is this hard or soft?

If you don't specify -H for hard or -S for soft, you are doing it for both. Look at this:

1.- Checking the hard limit:
luis@starseedstation:~$ ulimit -Hn
524288

2.- Checking the soft limit:
luis@starseedstation:~$ ulimit -Sn
1024

3.- Modifying the limits:
luis@starseedstation:~$ ulimit -n 1025

4.- Checking the limits again:

luis@starseedstation:~$ ulimit -Hn
1025
luis@starseedstation:~$ ulimit -Sn
1025

If I raise a limit with $ ulimit -n 1025 it works, then I try to lower the
limit back to its default 1024 with $ ulimit -n 1024 I get an error. Why?

1.- What's the exact error you are getting?
2.- What user is running the command?
3.- What distro and version are you running?

To edit the /etc/security.limits.conf is it safe to use vim/nano?

While you put the right information in there, there will no harm.

Regards,
Luis.

WarrenUK

@luisviveropena said:

If I raise a limit with $ ulimit -n 1025 it works, then I try to lower the
limit back to its default 1024 with $ ulimit -n 1024 I get an error. Why?

1.- What's the exact error you are getting?
2.- What user is running the command?
3.- What distro and version are you running?

In a fresh terminal:

$ ulimit -n 1025 works ok
$ ulimit -n 1024 works ok
$ ulimit -n 1025 error
bash: ulimit: open files: cannot modify limit: Operation not permitted

luisviveropena

Hi @WarrenUK ,

Please provide the requested information, so I can try to help you.

1.- What user is running the command? Is it a normal user, is it root?

2.- What distro and version are you running?

3.- Check /etc/security/limits.conf for limits.

Regards,
Luis.

WarrenUK

1. normal user
2. Kubuntu 19.10
3. Nothing is set in limits.conf

Here is my output for ulimit -a

core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 31181
max locked memory (kbytes, -l) 65536
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 31181
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited

I'm confused by what is a hard and soft limit in this output?

WarrenUK

Hi.

I've had another play around. This is confusing me.

$ ulimit -H -n
1048576
$ ulimit -S -n
1024
$ ulimit soft
$ ulimit -n 10000
$ ulimit -H -n
100000

I thought the soft limit could be set up and down up to the hard limit? I can set the soft limit upwards once and then progressively lower it down and down but I can never increase it again as the hard limit comes down with the soft limit even though I am not choosing the hard limit at the terminal.

luisviveropena

Hi @WarrenUK ,

I thought the soft limit could be set up and down up to the hard limit?

That's correct.

I can set the soft limit upwards once and then progressively lower it down
and down but I can never increase it again as the hard limit comes down
with the soft limit even though I am not choosing the hard limit at the terminal.

Nop, that happens because you are lowering down the hard limit, here:

$ ulimit -n 10000

When you don't specify if it's soft or hard, the ulimit command will affect both.

Regards,
Luis.

WarrenUK

Hi Luis.

So if I do

$ ulimit soft
$ ulimit -n 10000 <<<< this will set both hard and soft limit at the same time?

What is the $ ulimit soft command for then?

Many thanks.

luisviveropena

Hi Warren,

So if I do

>

$ ulimit soft
$ ulimit -n 10000 <<<< this will set both hard and soft limit at the same time?

Yes, that's right.

What is the $ ulimit soft command for then?

If you want to rise the soft limit to 10000, you do the following:

ulimit -Sn 10000

Look at this:

luis@starseedstation:~$ ulimit -Sn
1024
luis@starseedstation:~$ ulimit -Hn
524288
luis@starseedstation:~$ ulimit -Sn 10000
luis@starseedstation:~$ ulimit -Sn
10000
luis@starseedstation:~$ ulimit -Hn
524288
luis@starseedstation:~$

Regards,
Luis.