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Accepted
Tomas.R
Asked: 2020-12-05 09:07:20 +0800 CST

The size of the file set as a limit in limits.conf

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I edited the /etc/security/limits.conf file to limit the size of files that a user "student" can create:

@student        hard    fsize           3001
@student        soft    fsize           2001

Now when I login as a "student" and try to create a few files to see how big of a size I can create them I encounter this weird behaviour :

student@node1:~$ ulimit -f
2001

student@node1:~$ dd if=/dev/zero of=file1 bs=1KB count=2049
2049+0 records in
2049+0 records out
2049000 bytes (2.0 MB, 2.0 MiB) copied, 0.0127504 s, 161 MB/s


student@node1:~$ dd if=/dev/zero of=file2 bs=1KB count=2050
File size limit exceeded (core dumped)

I then check their sizes :

student@node1:~$ ls -l
-rw-rw-r--  1 student student 2049000 Dec  4 16:56 file1
-rw-rw-r--  1 student student 2049024 Dec  4 16:57 file2

Why am I allowed to create files this big ? In the dd command I can describe the max size as bs=1KB count=2049. Shouldn't it be bs=1KB count=2001 since I have put "2001" in /etc/security/limits.conf ?

files ulimit

1 Answers

  1. Best Answer

    The ulimit value appears to be in kibibytes (2001 x 1024 = 2049024 bytes) whereas bs=1KB is kilobytes (2049 x 1000 = 2049000 bytes). The dd suffix for kibibytes is just K (or k) not KB.

    So

    :~$ ulimit -f
2001

:~$ dd if=/dev/zero of=file1 bs=1k count=2001
2001+0 records in
2001+0 records out
2049024 bytes (2.0 MB, 2.0 MiB) copied, 0.0210431 s, 97.4 MB/s

:~$ dd if=/dev/zero of=file2 bs=1k count=2002
File size limit exceeded (core dumped)

:~$ ls -l file1 file2
-rw-rw-r-- 1 username username 2049024 Dec  4 13:15 file1
-rw-r--r-- 1 username username 2049024 Dec  4 13:15 file2
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