alexalmazan.com

The following provides output concerning connections to your web server in a ‘TIME WAIT’ status.

netstat -antlp | grep :80 | grep -v TIME_WAIT | awk '{print $5}' | awk -F : '{print $1}' | sort | uniq -c | sort -n | tail -n15

Large number of these connections from numerous sources are indicative of a denial of service attack. To remedy this, the following will place all sources identified into your software firewall:

for i in `netstat -antlp | grep :80 | grep -v TIME_WAIT | awk '{print $5}' | awk -F : '{print $1}' | sort | uniq -c | sort -n | tail -n15 | awk '{print $2}'` ; do iptables -A INPUT -s $i -j DROP ; done 

This command syntax evaluates the Plesk maillogs and gives an account of the domains recieveing the most mail

cat /usr/local/psa/var/log/maillog | grep -o 'to=.*@.*' | sed 's/to=.*@//' | sort | uniq -c | sort -rn | head 

Establishing software RAID is done through the use of ‘mdadm’ via the CLI

mdadm -C ‘RAID dev’ -l ‘level’ -n ’#of disks/partitions’

Here is an example designating device /dev/md0 set to RAID 1 amongst the partitions /dev/sda5 and /dev/sda6

mdadm --create /dev/md0 -l 1 -n 2 /dev/sda5 /dev/sda6

once done you can check the status in real time with

cat /proc/mdstat

[root@server1]# cat /proc/mdstat%

personalities : {raid1} md0 : active raid1

Once the RAID is active, it requires a file system and label. Create a file system and label on the new container with the following syntax

[root@server1]#mke2fs -j /dev/md0 -L raid1

Next, get the device mounted and available upon the next server reboot with

[root@server1]_tail -i /etc/mtab >> /etc/fstab 

This will add to the /etc/fstab file or manually edit /etc/fstab with something similar to

/dev/md0    /mnt    ext3    rw    0 0

The following command sequence using ‘mdadm’ fails drive in the array-

mdadm /dev/md0 -f /dev/sda5

removes failed drive

[root@server1]#mdadm /dev/md0 -r /dev/sda5

re adds failed drive

mdadm /dev/md0 -a /dev/sda5 

mdadm—detail

FDISK RAID example

fdisk /dev/sda n

create extended

select all sizes n

once the partitions are written, ‘partprobe’

(ex. device creation in /dev/) mknod sda6 b 8 6

mdadm _X

DONT forget to issue ‘partprobe’ after fdisk

mdadm -C /dev/md1 -l 5 -n 3 -x 1 /dev/sda{7.8.9.10}

n is the number of components -x spare components then fail a drive with

mdadm /dev/md1 -f /dev/sda7 

watch -i /cat/proc/mdstat to see the failure

Enabling file system quotas can be completed in a few steps.

1.	add to /etc/fstab usrquota or grpquota

After the changes to fstab, you will have to remount the partition

2.	mount -o remount /

Next generate the quota files

3.	quotacheck -cg / -compile a database of usage statistics on the FS for users, -u can also be used for users

Turn quota on

4.	quotaon / (quota on -ap show all status on)

Use ‘repquota’ to review a report of usage

5.	repquota -a all partitions’ -ag for group

Use edquota for edits

6.	edquota ‘user’

soft limit governs grace period hard limit is a strict policy

edquota -t this will permit you to modify the block and inode grace period for soft limits (typically one block is one kilobyte)

This table represents the order in which shell attributes are inherited

/etc/skel	default template for a new added users home directory
/etc/profile	sets environmental variables used by all users
/etc/profile.d	contains scripts specific to certain RPMS
/etc/bashrc	contains global aliass and system settings
~/.bash_profile	contains user environement settings and can be set to auto start programs at login
~/.bashrc	contains user aliases and functions