Routine task change ip address on remote host without cut off. There are a lot of possibilites i.e. from reboot with new ip address to some fancy stuff with cron job. But there is a one method to make it clear and elegant.

Simply set:

echo 1 > /proc/sys/net/ipv4/conf/all/promote_secondaries

and set secondary/new ip address:

ip addr add <my_new_ip_addr_with_netmask> dev <my_interface>

delete old ip address:

ip addr del <my_old_ip_addr_with_netmask> dev <my_interface>

and without promote_secondaries option you will end up with no net, but fortunately secondary ip address become primary. Of course you should take care to of change default route if necessary i.e. by putting new default route with higher metric, so it becomes active when old ip will be deleted.


New look and feel

Sun 29 June 2014 by admin

After couple months of inactivity I am starting with new look of blog site. It's not only a new theme, but it's completly rewrite engine. No more complexity of Wordpress on top of Varnish,Nginx,PHP,MySQL just pure static content generated by Pelican. Static website is served ...

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Jesień Linuksowa 2013

Tue 08 October 2013 by admin

Tym razem po drugiej stronie mikrofonu:

Zaopiekuj się moimi logami
Witold Duranek

więcej na: http://jesien.org/2013/pl/agenda

Zapraszam,

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Zerofree your filesystem

Sat 28 September 2013 by admin

Lets assume that you have file image:

dd if=/dev/zero of=file.1 bs=4k count=128

on top of it you create filesystem ext3/ext4

mkfs.ext4 /root/file.1

mount it, create remove some files etc. and you gonna make it more space efficient, that's ...

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Some notes about memory ballooning in VMware

Sun 01 September 2013 by admin

Couple days ago I found out that memory usage grow rapidly on one server. After couple minutes of investigation, it was clear that memory balloon take place. Of course it will happen only if you have vmware tools installed. To find out what was happening, you can look at vmware ...

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Manage your hard disks

Sun 04 August 2013 by admin

Make one step forward after rediscovering newly added hard disk, simply how to resize it. In virtual world simply put the new disk size, but how to reflect this change in guest operating system:

echo 1 > /sys/block/<devname>/device/rescan
partprobe

Continuing how to make them unavailable first to ...

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Sign your scripts

Sun 30 June 2013 by admin

Remote command execution from one host to another is nothing new in more complex infrastructure. It is usually going to happen at low user level privilege and it's also password less ssh communication based on ssh keys. But what happens when ssh keys leaked or this account was compromised ...

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VMware disk cloning

Sun 16 June 2013 by admin

Using free VMware vSphere Hypervisor doesn't give us a chance to easily clone virtual machines disks and cope with thin provision disks. But we could leverage administration to CLI (shell) and there we have command called: vmkfstools. This command is used to manage virtual disks i.e. create, convert ...

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linux nocache idea

Sun 09 June 2013 by admin

Each time when you read file it's content is put into cache:

# grep -w "Cached" /proc/meminfo
Cached:           255220 kB
# cat sample.file >/dev/null
# grep -w "Cached" /proc/meminfo
Cached:           357628 kB

of course it happens when there is enough free memory. But imagine situation when you read ...

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cisco tips #1

Sun 09 June 2013 by admin
  • replace default escape character (ctrl+shift+6) to ctrl+c:
line vty 0 4
  escape-character 3
  • show logging timestamps in configured timezone
service timestamps log datetime localtime year
  • secure your configuration

http://www.cisco.com/en/US/docs/ios/sec_user_services/configuration/guide/sec_autosecure.html

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