# dpkg -l|grep ssmtp
iF  ssmtp                                  2.64-4fakesync1                                 extremely simple MTA to get mail off the sys

if ssmtp is not installed yet, install it by using

# apt-get install ssmtp

If you are using Gmail account , change the root, authuser, and authpass options to the email address, username, and password of your email account. If you’re using another mail service you’ll need to change mailhub to the relevant SMTP server.

edit /etc/ssmtp/ssmtp.conf and add these lines

--------------------------------------------
root=alert@example.com
mailhub=smtp.example.com:587
rewriteDomain=
hostname=smtp.example.com:587
UseSTARTTLS=YES
UseTLS=YES
AuthUser=alert@example.com
AuthPass=password
AuthMethod=LOGIN
FromLineOverride=YES # optional
--------------------------------------------

Change the ‘From’ text by editing /etc/passwd to receive mail from ‘root@server1.example.com’ instead of just ‘root’.
# chfn -f root@server1.example.com root

edit /etc/ssmtp/revaliases and add this line or add more line for another user
--------------------------------------------
# sSMTP aliases
#
# Format:    local_account:outgoing_address:mailhub
#
# Example: root:your_login@your.domain:mailhub.your.domain[:port]
# where [:port] is an optional port number that defaults to 25.
root:alert@example.com:smtp.example.com:587
--------------------------------------------

to test it

# echo “test send email using ssmtp|mail -s “TEST” alert@example.com

once you are able to receive that test message, proceed to edit /etc/hosts.allow and add these 2 lines, so you will be notified if someone login to your sever

--------------------------------------------
SSHD: ALL: spawn (/bin/echo "SSH connection to %H from %h[%a]" | \
/usr/bin/mail -s "SSH Login Alert [server1.example.com]" alert@example.com)
--------------------------------------------

I’d seen this message before, but I headed over to Red Hat’s site for more details. Generally, the ip_conntrack_max is set to the total MB of RAM installed multiplied by 16. However, this server had 4GB of RAM, but ip_conntrack_max was set to 65536:

# cat /proc/sys/net/ipv4/ip_conntrack_max
65536

If you want to check your server’s current tracked connections, just run the following:

# cat /proc/sys/net/ipv4/netfilter/ip_conntrack_count

If you want to adjust it, just run the following as root:
# echo 131072 > /proc/sys/net/ipv4/ip_conntrack_max

If you want to find out how many sessions are open right now:
# wc -l /proc/net/ip_conntrack

-There is existing LVM partition 50GB in total and has been used up 5GB
-We will reduce the LVM partition from 50GB to 10GB
-We need to unmount the FS before we can proceed
-Please do proper backup before proceed as there might be chances that you would lose your data

Output from df -h /media/data:

Filesystem                                                     Size  Used Avail Use% Mounted on
/dev/mapper/vgdata-lvdata                       50G  5.0G   42G  11% /media/data

Example current usage taken from df -h is 5G and wanted to be shrunk to 10G
# umount /dev/vgdata/lvdata
# e2fsck -f /dev/vgdata/lvdata
# resize2fs /dev/vgdata/lvdata 8G
# e2fsck -f /dev/vgdata/lvdata
# lvreduce -L 10G /dev/vgdata/lvdata
# e2fsck -f /dev/vgdata/lvdata
# resize2fs /dev/vgdata/lvdata
# e2fsck -f /dev/vgdata/lvdata
# mount -a

——————-
Increasing(online)::
——————-
Scenario:
-We would like to increase /add in another 5GB to /dev/vgdata/lvdata

lvextend -L +5G /dev/vgdata/lvdata
resize2fs /dev/vgdata/lvdata

Oct 24 03:01:43 ns1 named[30660]: client 200.23.242.196#35545: query: parentsascoaches.net IN MX
Oct 24 03:01:43 ns1 named[30660]: client 80.86.96.1#58395: query: mx1.clients.netdns.net IN A
Oct 24 03:01:43 ns1 named[30660]: client 195.175.39.118#60651: query: abs-pos.com IN MX

mysql> set global max_connections=400;

you can check the results using this command

mysql> show global variables;

always be reminded that parameter has been setup using above command will be not persist across restart, you need to put the parameter in /etc/my.cnf so the changes will persist across reboot.

————————————————–
Bus 001 Device 002: ID 148f:2570 Ralink Technology, Corp. 802.11g WiFi
Device Descriptor:
bLength 18
bDescriptorType 1
bcdUSB 2.00
bDeviceClass 0 (Defined at Interface level)
bDeviceSubClass 0
bDeviceProtocol 0
bMaxPacketSize0 64
idVendor 0x148f Ralink Technology, Corp.
idProduct 0×2570 802.11g WiFi
bcdDevice 0.01
iManufacturer 1 Ralink
iProduct 2 802.11g WLAN
iSerial 0
bNumConfigurations 1

—————————————————————————-
i knew that centos has rt2500usb module build in as module in the kernel itself and it’s loaded automatically when booting up, but the strange thing i cannot associate with any ap that is working fine with other wifi adapter, i thought there must be something wrong with the kernel, because i’m using a non usual kernel on my machine , it’s a “2.6.18-128.1.1.el5.028stab062.3PAE” , it’s a openvz kernel , but it was gave the same results when i boot up with standard kernel

wlan0: authentication with AP xx:xx:xx:xx:xx:xx timed out
and
something like cannot associate to the AP itself

had several times googling and here are the solutions, quite simple solutions in fact
-)download the new driver, looks like there are some incompatibility/bugs with the current driver,
drivers are downloadable through http://www.ralinktech.com/ralink/Home/Support/Linux.html
and compile it
-)prevents current driver being activated during booting, just simply put the module into /etc/modprobe.d/blacklist, it should be something like this
—————————————————————————-
blacklist rt2500usb
—————————————————————————-
-)#reboot
-)check the module whether the new module/driver brought up after rebooted
rt2570 163712 0
-)check if there any new interface appearing after executed ifconfig -a
—————————————————————————-

rausb0 Link encap:Ethernet HWaddr 00:00:00:00:00:00
BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
—————————————————————————-
wala!!!, all seems to be working perfectly , after it’s can associated with the AP , and got the ip address by using dhclient

Reference:

http://harusharris.blogspot.sg/2009/08/compex-wlu54g-finally-on-centos-52.html

Tools required:
-)Linux OS running on your Server/Computer/Notebook with root access
-)5 minutes of less

-)Open your /etc/sysctl.conf file
-)Add this line
kernel.panic = 10
-)Save your /etc/sysctl.conf file, you can either reboot your machine or execute this command to reload sysctl to your kernel
sysctl -p

i found that the software RAID that we are using on that server, was being resynchronizing between all disks in that RAID array, and it’ was very very super duper slow, it’s only about 4.5KB/Sec!!!! yuck… , and tried to bring up one of VPS hosted on that server, it was always gives me “cannot lock VE” , there was no other options , i need turned off automatic startup for that virtuozzo service when server booting up

#chkconfig –level 345 vz off

and initiated “shutdown -r now” , not worked, damn!!…. tried “shutdown -r -f -n now” also gave me that the server is shutting down, wait for 3 minutes…., 10 minutes…., 25 minutes…. yuck, enough .. called up data center and ask them to repeat hard reboot sequence , and after rebooted, sshed to server, check for RAID synchronization ,using more /proc/mdstat

———————————————————————————————————–

Personalities : [raid1]
md0 : active raid1 sdb2[1] sda2[0]
4192896 blocks [2/2] [UU]

md2 : active raid1 sdb3[1] sda3[0]
479998016 blocks [2/2] [UU]
[>....................] resync = 0.7% (3745728/479998016) finish=139.4min speed=56924K/sec

md1 : active raid1 sdb1[1] sda1[0]
4192832 blocks [2/2] [UU]

———————————————————————————————————–

Hmmmm… much much better….after RAID synchronization completed, bring up VZ service and all VPSes back up for serving their “Masters” fiuuuh….

unfortunately it was not solved the problem completely, some of customers that have access to VZ/Power Control Panel , complained that they had problem accessing Plesk Control Panel (8443), login successful but they were always got this error message,

“Plesk is not allowed”

quick investigations found that this only affected to customer that using Virtuozzo offline management, by turning this offline management off, there is no issue accessing Plesk Control Panel, but they will lose capability to reboot,shutdown VPS remotely from VZ/Power Control Panel, these are some step by step in how to rectify the issue,

check Vzagagent status and restart it

#vzagent_ctl status

the results should be similar like this

vzagent (pid 28742 21104 20602 12985 12980 11195 11071 10749 10571 10375 10374 9214 9213 9206 9205 9203 9201 9200 9199 9198 9189 9185 9184 9182 9181 9180 9179 9178 9177 9176 9175 9174 9173 9172 9171 9170 9169 9168 9167 9166 9165 9164 9163 9162 9161 9160 9159 9158 9156 9155 9154 9153 9152 9151 7146 2461) is running…

and try to restart it

#vzagent_ctl restart

and if this also does not solve the problem with offline management still active, just try to restart Service Container,

#vzctl restart 1

otherwise you need to reinstall Service Container (VE 1), fortunately in my case , no need to reinstall that Service Container

References:

http://forum.parallels.com/showthread.php?t=84022

http://kb.parallels.com/en/659