[root@host ~]# dd if=/dev/zero of=/swapfile bs=1024 count=1048576
1048576+0 records in
1048576+0 records out
[root@host ~]# sync
[root@host ~]# mkswap /swapfile
Setting up swapspace version 1, size = 1073737 kB
[root@host ~]# swapon /swapfile
[root@host ~]# echo “/swapfile swap swap defaults 0 0″ >> /etc/fstab

Generate ifcfg-eth1 307-366 configs.

touch ifcfg-eth1:{307..366}
for f in ifcfg-eth1:{307..366}; do cat origfile > “$f”; done
for f in eth1:{307..366}; do echo “DEVICE=$f” >> “ifcfg-$f”; done
for f in {307..366}; do echo “IPADDR=aaa.bbb.ccc.$((f-239))” >> “ifcfg-eth1:$f”; done

origfile contains:

GATEWAY=eee.fff.ggg.hhh
TYPE=Ethernet
BOOTPROTO=none
NETMASK=255.255.255.192

iostat syntax for disk utilization report

iostat -d -x interval count

-d : Display the device utilization report (d == disk)
-x : Display extended statistics including disk utilization

interval : It is time period in seconds between two samples . iostat 2 will give data at each 2 seconds interval.

count : It is the number of times the data is needed . iostat 2 5 will give data at 2 seconds interval 5 times

Display 3 reports of extended statistics at 5 second intervals for disk

Type the following command:

# iostat -d -x 5 3

Output:

[root@vari Desktop]# iostat -d -x 5 3

Linux 2.6.18-128.7.1.el5xen (vari.taashee.com) 08/26/2009 _i686_ (2 CPU)

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util

sda 2.41 12.42 3.27 5.37 134.84 142.70 32.13 0.12 14.04 1.83 1.58

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util

sda 0.00 1.60 0.00 0.40 0.00 16.00 40.00 0.00 0.00 0.00 0.00

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util

sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Where,

rrqm/s : The number of read requests merged per second that were queued to the hard disk
wrqm/s : The number of write requests merged per second that were queued to the hard disk
r/s : The number of read requests per second
w/s : The number of write requests per second
rsec/s : The number of sectors read from the hard disk per second
wsec/s : The number of sectors written to the hard disk per second
avgrq-sz : The average size (in sectors) of the requests that were issued to the device.
avgqu-sz : The average queue length of the requests that were issued to the device
await : The average time (in milliseconds) for I/O requests issued to the device to be served. This includes the time spent by the requests in queue and the time spent servicing them.

svctm : The average service time (in milliseconds) for I/O requests that were issued to the device
%util : Percentage of CPU time during which I/O requests were issued to the device (bandwidth utilization for the device). Device saturation occurs when this value is close to 100%.

How do I interpret the output result for optimization?

First you need to note down following values from the iostat output:

1. The average service time (svctm)
2. Percentage of CPU time during which I/O requests were issued (%util)
3. See if a hard disk reports consistently high reads/writes (r/s and w/s)

If any one of these are high, you need to take one of the following action:

Get high speed disk and controller for file system (for example move from SATA I to SAS 15k disk)
Tune software or application or kernel or file system for better disk utilization
Use RAID array to spread the file system

du –max-depth=1 $PWD | sort -n -r
du -H –max-depth=1 $PWD

“-H” – produce human readable format sizes (like: 1K 10M 1G)

A good and short one liner using xargs

du -s ./* | sort -n| cut -f 2-|xargs -i du -sh {}

This will sort the folders according to size and display them in human readable format… to reverse the list
use sort -nr option.

yum install vsftpd

[root@shifu ~]# cat /etc/vsftpd/vsftpd.conf | grep -v ^#
anonymous_enable=NO # disable anonymous account
local_enable=YES # enable local users
write_enable=YES # enable uploading files
local_umask=022 # mask
dirmessage_enable=YES
xferlog_enable=YES # log messages
connect_from_port_20=YES
xferlog_std_format=YES
idle_session_timeout=600
chroot_list_enable=YES # chroot users into their own dir
listen=YES

pam_service_name=vsftpd
userlist_enable=YES
tcp_wrappers=YES

/etc/vsftpd/chroot_list contains a list of all users that will be in chroot

How to upgrade MySQL 5.0 to MySQL 5.1 in a cPanel server

Login as root and edit /var/cpanel/cpanel.config.

Replace :

mysql-server=5.0 with
mysql-server=5.1

Finally run: /scripts/mysqlup

net.ipv4.tcp_ecn = 0
net.ipv4.conf.default.rp_filter = 1
#kernel.sysrq = 1
kernel.core_uses_pid = 1

net.ipv4.conf.default.rp_filter = 0
net.ipv4.conf.all.rp_filter = 0
net.ipv4.conf.eth0.rp_filter = 0

net.ipv4.neigh.default.gc_thresh1 = 65535
net.ipv4.neigh.default.gc_thresh2 = 65535
net.ipv4.neigh.default.gc_thresh3 = 65535

kernel.core_uses_pid = 1
#Default ttl
net.ipv4.ip_default_ttl = 255

#No uptime
net.ipv4.tcp_timestamps=0

#Forwarding
net.ipv4.ip_forward = 1

net.ipv4.tcp_ecn = 0
net.ipv4.conf.default.rp_filter = 1
kernel.core_uses_pid = 1

#Connection max numer
net.ipv4.ip_conntrack_max = 65535

#Against DDOS //6169=0x1819
net.ipv4.icmp_ratelimit=0
net.ipv4.icmp_ratemask=6169

#Disabling of ICMP echo-reply directed to Broadcast addresses // against scanning
net.ipv4.icmp_echo_ignore_broadcasts=1