regarding command "ulimit"

[deepak_cucek]

Hi

i am totally new to this forum as well as linux...
as per my knowledge by using "ulimit" we can restrict the size of file that can create by user.

but in one folder i make the ulimit as 1kb by "ulimit -f 1"
but still i can create the file with more than 1kb ..
i need completely user need to prevent for creating file in the particular folder

[sorry for bad english]

[kakariko81280]

If you need to prevent a user from creating files in a directory, then you should use chmod rather than ulimit.

chris@angua:~$ mkdir test
chris@angua:~$ ls -la test
total 8
drwxr-xr-x  2 chris chris 4096 2008-02-04 13:56 .
drwx------ 84 chris chris 4096 2008-02-04 13:56 ..
chris@angua:~$ touch test/file1
chris@angua:~$ ls -la test
total 8
drwxr-xr-x  2 chris chris 4096 2008-02-04 13:56 .
drwx------ 84 chris chris 4096 2008-02-04 13:56 ..
-rw-r--r--  1 chris chris    0 2008-02-04 13:56 file1
chris@angua:~$ chmod 500 test
chris@angua:~$ ls -la test
total 8
dr-x------  2 chris chris 4096 2008-02-04 13:56 .
drwx------ 84 chris chris 4096 2008-02-04 13:56 ..
-rw-r--r--  1 chris chris    0 2008-02-04 13:56 file1
chris@angua:~$ touch test/file2
touch: cannot touch `test/file2': Permission denied
chris@angua:~$

The permissions in the first column of the 'ls' command are Read, Write and eXecute. If I use chmod to remove the write permission on the directory then I can no longer create files there.

In this example I keep ownership of the test directory. This means I can change the permissions to allow me to write files again. To prevent this I would need to change ownership of the directory to another user. Use 'chown' to do that.

Let us know how you get on,

Chris...

[deepak_cucek]

thanx buddy
but it is not happening here...
NB: am entered as "root" user

[kakariko81280]

Trying to prevent a root user from doing whatever they please is usually a waste of time. There are such things as SELinux which you may be able to use but I've never tried them.

A more practical way is to remove the need to be root in order to do what you are trying to achieve. If root access is required for a part of the task then sudo can be used to allow normal users to perform specific tasks as root.

Can you tell us more about what you are trying to do. Then we may be able to help you find a simple way to do it.

Let us know how you get on,

Chris...

[deepak_cucek]

ok i will explain..

am testing a tool that only works in "root" user
the tool is creating one file in some folder...
i need to check what will happen if tool try to generate a file in to a folder..
where no permission or any other similiar conditions..
i heard by using ulimit we can restrict the size of file...
but still tool succesfully generated file..

[kakariko81280]

You may already have your answer: If you are root you can ignore permissions for the most part and I would guess that is why ulimit isn't working either.

One way to actually have this fail would be to make a small read only filesystem and try to write your file there.

chris@angua:~/src$ sudo -s
[sudo] password for chris:
root@angua:~/src# cd
root@angua:~# dd if=/dev/zero of=./disk.img bs=1024 count=1024
1024+0 records in
1024+0 records out
1048576 bytes (1.0 MB) copied, 0.00394552 seconds, 266 MB/s
root@angua:~# losetup /dev/loop0 ./disk.img
root@angua:~# mkfs.ext2 /dev/loop0
mke2fs 1.40.2 (12-Jul-2007)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
128 inodes, 1024 blocks
51 blocks (4.98%) reserved for the super user
First data block=1
Maximum filesystem blocks=1048576
1 block group
8192 blocks per group, 8192 fragments per group
128 inodes per group

Writing inode tables: done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 28 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
root@angua:~# mkdir /mnt/test
root@angua:~# mount /dev/loop0 /mnt/test -o ro
root@angua:~# touch /mnt/test/file1
touch: cannot touch `/mnt/test/file1': Read-only file system
root@angua:~# umount /mnt/test
root@angua:~# losetup -d /dev/loop0
root@angua:~# rm disk.img

Note the "-o ro" option on mount sets the filesystem to read only. The root user can still work around that so don't rely on it, but it should fail for now.

Let us know how you get on,

Chris...

[deepak_cucek]

i solved my problem by "ulimit" it self
actually i didnt know about the fact that "ulimit" will only in that particular session.
i set the ulimit
then run the tool from the same session
tool is crashing......