Ajay, Author at IT Security and Internet

add static route in Cantos and make sure it wont loose after reboot

AjayFebruary 7, 2013

1. Adding Routes

[root@localhost ~]# route add -net 10.4.3.0 netmask 255.255.255.0 gw 192.168.129.55
[root@localhost ~]#

[root@localhost ~]# route add -net 10.4.2.0 netmask 255.255.255.0 dev eth0
[root@localhost ~]#

2. Show routing table

[root@localhost ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.129.0 0.0.0.0 255.255.255.0 U 1 0 0 eth0
10.4.3.0 192.168.129.55 255.255.255.0 UG 0 0 0 eth0
10.4.2.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
0.0.0.0 192.168.129.2 0.0.0.0 UG 0 0 0 eth0
[root@localhost ~]#

if you dont wanna loose, you can add above command to /etc.rc.local

or try this way

add routes in route-eth0 file

static routes for the eth0 interface would be stored in the /etc/sysconfig/network-scripts/route-eth0 file. The route-interface file has two formats: IP command arguments and network/netmask directives.

The following is a sample route-eth0 file using the IP command arguments format. The default gateway is 192.168.0.1, interface eth0. The two static routes are for the 10.10.10.0/24 and 172.16.1.0/24 networks:

default 192.168.0.1 dev eth0
10.10.10.0/24 via 192.168.0.1 dev eth0
172.16.1.0/24 via 192.168.0.1 dev eth0

Static routes should only be configured for other subnets. The above example is not necessary, since packets going to the 10.10.10.0/24 and 172.16.1.0/24 networks will use the default gateway anyway. Below is an example of setting static routes to a different subnet, on a machine in a 192.168.0.0/24 subnet. The example machine has an eth0 interface in the 192.168.0.0/24 subnet, and an eth1 interface (10.10.10.1) in the 10.10.10.0/24 subnet:

Find out the IP address of eth0 and display IP only

AjayFebruary 7, 2013

Now you just wanted the IP address, use grep to get the IP:
$ /sbin/ifconfig eth0| grep 'inet addr:'Output:

inet addr:192.168.2.1  Bcast:192.168.2.255  Mask:255.255.255.0

To get IP address from use cut command:
$ /sbin/ifconfig eth0 | grep 'inet addr:' | cut -d: -f2Output:

192.168.2.1  Bcast

Finally remove Bcast with awk
$ /sbin/ifconfig eth0 | grep 'inet addr:' | cut -d: -f2 | awk '{ print $1}'
Output:

192.168.2.1

Show a Table Of All Network Interfaces Using netstat Command

AjayFebruary 7, 2013

Type the following command:
$ netstat -i
Sample outputs:

Kernel Interface table
Iface   MTU Met   RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
eth0       1500 0   2697347      0      0 0       2630262      0      0      0 BMRU
lo        16436 0      2840      0      0 0          2840      0      0      0 LRU

How can i see if an ethernet interface is up/down linux centos

AjayFebruary 7, 2013

watch ip link show

ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 50:e5:49:45:3f:96 brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:0a:cd:20:31:4a brd ff:ff:ff:ff:ff:ff
4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:0a:cd:20:30:c7 brd ff:ff:ff:ff:ff:ff

Fix: Cyrus-IMAP Logging region out of memory cirus imap

AjayFebruary 7, 2013

I found out that the Cyrus-IMAP’s database is flagging with errors as below:

[root@mail ~]# tail -n 100 -f /var/log/maillog

Mar 24 10:36:14 mail lmtpunix[4017]: executed
Mar 24 10:36:14 mail lmtpunix[4017]: DBERROR db4: Logging region out of memory; you may need to increase its size
Mar 24 10:36:14 mail lmtpunix[4017]: DBERROR: opening /var/lib/imap/deliver.db: Cannot allocate memory
Mar 24 10:36:14 mail lmtpunix[4017]: DBERROR: opening /var/lib/imap/deliver.db: cyrusdb error
Mar 24 10:36:14 mail lmtpunix[4017]: FATAL: lmtpd: unable to init duplicate delivery database
Mar 24 10:36:14 mail master[4664]: process 4017 exited, status 75
Mar 24 10:36:14 mail master[4664]: service lmtpunix pid 4017 in READY state: terminated abnormally
Mar 24 10:36:14 mail master[4018]: about to exec /usr/lib/cyrus-imapd/lmtpd

It turned out that the Cyrus-IMAP service runs out of log memory. So here comes the need to change the default setting and create a bigger cache and log memory regions of Cyrus-IMAP’s database as documented below.

Changing the default Logging region of Cyrus-IMAP servers database is easy.

Create a DB_CONFIG file is you have not done it yet.

[root@mail ~]# cat > /var/lib/imap/db/DB_CONFIG

set_cachesize 0 2097152 1

set_lg_regionmax 1048576

Stop the cyrus-imapd server, this is very important.

[root@mail ~]# /etc/init.d/cyrus-imapd stop

Backup the database to be recovered.

[root@mail ~]# rsync -auvp /var/lib/imap/db /root/db_backup.date

Recover the database that was changed.

[root@mail ~]# db_recover -h /var/lib/imap/db

Once the command above is successfully done, we can now start the Cyrus-IMAP service.

[root@mail ~]# /etc/init.d/cyrus-imapd start

Check the new cache and memory statitics and wether the new settings are set correctly.

[root@mail ~]# db_stat -h /var/lib/imap/db -m

[root@mail ~]# db_stat -h /var/lib/imap/db -l

Shoot a few emails and check the logs how it goes. If users are no receiving emails correctly, the server is now back online. Keep monitoring until you are certain that everything is now back to normal

Courtesy: http://i8n1.blogspot.com/2010/03/cyrus-imap-logging-region-out-of-memory.html