panic cannot login to linux

Panic ! Thats what occurs when a critical systems you manage cannot login , but the service was running properly.

Recently i do some changes on the /etc/security/limits.conf and it make all lockout. No SSH can be done, but all the service was running properly.

To the rescue, we need to login to the systems and revert back changes, and to do that we need to go into single mode.

We do on Centos 7.x systems which is the grub boot loader is different than the old version.

So how to do it step by step, and no panic. 

• Reboot your machine and immidiately go to rescue mode.
• Chose one boot options and press "e" to change the entry
• Look for below entry :
  linux16 /boot/vmlinuz-3.10.0-123.el7.x86_64 root=UUID=act2884249823928928392 ro  xxxxxx
• Change the ro to below 
  rw init=/sysroot/bin/sh
• Then continue the boot, press ctrl+x to do that. No worries, after finish you can reboot and the grub boot loader will be still the old one.
• once boot to single mode you need to mount the filesystem. do
  # chroot /sysroot/
• After this step you can revert back any settings you made to restore it to working state.
• On our side, its /etc/security/limits.conf
• After finish we can reboot the machine to production mode
  # reboot -f

That was no panic attack anymore if you know what you are doing.

Always make sure you have backup of the OS.

Or better way use Container these days. 

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IT Asset Management Software

Do you have ever experience trouble in managing your Assets in your organizatoin, especially within the scope of IT Assets like PC, laptop, accessories, etc which related to day to day operation ?

Manual will be using spreadsheets application available. More advance are using a specialized software which manage your assets and logs where about the assets and status.

Come the rescue, Snipeit asset management. Its a software based asset management with full feature to manage your assets and also come as a free open source software. Of course with free meanings, you can do it all by yourself to make it works, besides your skill on translate the documentation to working application.

Here you need to know that Snipeit application is a :
1. PHP based application
2. Need a database to function properly, eg. Mariadb or Postgresql.
3. Multiuser applicatoin
4. Support LDAP integration for corporate environment.
5. Can run both on Linux / Windows server as a web services

With this information, you should know what basic prerequisite needed.

For my journey, i come to Snipeit because organization i work for need an asset management software to manage all operation related activity and keep track of the asset owned by organization. This will be a second step after doing manual labour works using spreadsheets.

What i recommend to setup are using High Availability setup for uninterupted service, as these are web service, its easy to do the High Availablility setup, especially the web service part.

What can we do are using this design :

User ---------   HA Proxy               --->   Snipeit App 01   ----->    |    Snipeit Database
                       Load Balancer        --->  Snipeit APP 02    ----->    |

With this setup, access from user are load balanced between Snipeit AP 01 and 02 to provide high availability and load balancing within the application.

Working Snipeit IT ASSET Management Systems

The software we used are :
1. Centos 7.x
2. HA Proxy
3. Nginx
4. PHP7.2
5. MariaDB 10
6. Memcached

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Using Centos 5.x repo after EOL

We know Centos 5.x already EOL , and no update given.
But we sometimes still use the version as upgrade will be broke our application usage.

So problem arise when we need to install application package in that version. The repo is moved from main url of the release, and moved to vault.centos.org . To able to install from your yum package manager , we need to update the yum base url.

Here are some command to fix it.

sed -i 's/enabled=1/enabled=0/' /etc/yum/pluginconf.d/fastestmirror.conf
sed -i 's/mirrorlist/#mirrorlist/' /etc/yum.repos.d/*.repo
sed -i 's|#baseurl=http://mirror.centos.org/centos/$releasever|baseurl=http://vault.centos.org/5.11|' /etc/yum.repos.d/*.repo

With above command, yum config updated and you will be able to install package from yum repo and download all the dependencies.

Beware as the app no longer supported and might introduce security issue.

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Update lates gcc in centos 6.x

Opensource is great as we can compile it from source by our self. it just a command to be used like configure , make and make install. You got your new software ready to use.

But sometimes when compiling, some errors can happend and the cause is the compiler is outdated, especially if you want to try new software, and the software constantly updated with new technology being used especially the complier.

So we must upgrade our complier like gcc which is the default compiler in linux world.

My experience also show error when compiling, when using Centos 6.x , the gcc still in version 4.4.7 .

We will update our gcc in centos 6.x by following these steps :

# yum install -y centos-release-scl

# yum install -y devtoolset-3-toolchain

# scl enable devtoolset-3 bash

# gcc --version

With this you will got gcc 4.9.2 ready to use for compiling you source code.

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