Category: How Tos

Having a disk quota on a shared system is very useful, you can control how much data each user can store on the system. In this tutorial I will assume that you have many partitions on your system, we will work with the home directory partition for your Linux system.

Do the following:

Step 1)

touch /home/aquota.user
chmod 600 /home/aquota.user

Step 2)

Edit the /etc/fstab file, we want to add "usrjquota=aquota.user,jqfmt=vfsv0" as an option for the home partition such that the home partition line looks like the following line:

/dev/sda7 /home ext3 defaults,usrjquota=aquota.user,jqfmt=vfsv0 1 1

Step 3)

You can choose to reboot the system to update the changes we just made or run this command "mount -o remount /home" which will remount the partition with the changes.

Step 4)

We need to do a quota check which will calculate how much disk space each user is currently using. So run the following line:

quotacheck -vuma

Step 5)

We need to turn quota on, so run this line:

quotaon -avu

Step 6) Last step

We need to set a quota for each user on the Linux system run edquota followed by the username.

Example "edquota pywong"

You should see something like this:

Disk quotas for user pywong (uid 1128):
  Filesystem                   blocks       soft       hard     inodes     soft     hard
  /dev/sda7                    473452    1000000    1500000        476        0        0
  /dev/sdb1                    296004   15000000   20000000        413        0        0
  /dev/sdb2                         0          0          0          0        0        0

When we use the edquota command this will most likely open it using a text editor called vi, you many need to read up on how to use vi for editing if you do not already know how to use it.

We want to edit the Filesystem line that matches our line for the home directory, in this case it’s the line with /dev/sda7, we want to edit the soft column and the hard column. 1000000 = 1GB and 1500000 = 1.5GB. You want the hard quota to be bigger than the soft quota, when user hit the soft quota they will get warning and if they hit the hard quota they will get error messages and the system will not let the user write anymore files.

The Linux OS the tends keep Cached memory because the it decides that the Cached memory is being used and is needed which can lead to memory issues and slow down your system.

To fix this problem you can force the system to free up the stored Cached memory.

Create a script called /usr/local/bin/clearcache.sh with the following two lines:

#!/bin/sh
sync; echo 3 > /proc/sys/vm/drop_caches

run "crontab -e" and add the following line:

0 * * * * /usr/local/bin/clearcache.sh

Also make the script executable by running “chmod +x /usr/local/bin/clearcache.sh”

This should clear the Cached memory every hour.

This will delete all files and directories old than 7 days within /tmp or other directory you specify, it will only look for files within that directory and not sub-directories.

find /tmp/ -maxdepth 1 -mtime +7 -exec rm -rf {} ;

• -maxdepth mean how deep to look for files.
• -mtime means the modified time.

This will list all the files that the first command would have deleted without actually deleting the files.

find /tmp/ -maxdepth 1 -mtime +7

Be very careful with the first command, it could render your system useless and delete other files. Do not use “/tmp/.*”, it could delete files outside of your directroy.

Protecting yor SSH server from brute force attacks will reduce the chance of someone gussing your password to your server or workstation. One way of doing that is to use IPTables, another way is to change the default port your SSH server is listening on, in this artical I will be show you how to do the IPTables route.

Put the following in /etc/sysconf/iptables and /etc/sysconf/ip6tables:

-A INPUT -p tcp -m tcp --dport 22 -m state --state NEW -m recent --set --name SSH
-A INPUT -p tcp -m tcp --dport 22 -m state --state NEW -m recent --update --seconds 60 --hitcount 5 --rttl --name SSH -j DROP
-A INPUT -p tcp -m tcp --dport 22 -m state --state NEW -j ACCEPT


restart iptables

/bin/systemctl restart iptables.service
/bin/systemctl restart ip6tables.service


This will drop connections after it has failed 5 times within the last 60 seconds.