Recovering Linux without getting into rescue mode

In large organizations, mostly the servers would be managed remotely through the console (ilo/drac/imm). The large company's also change the root password on all servers periodically which mostly happen through scripts.  If, due to any reason, the root password is not updated on server and if the server crash due to any file system related issues, the system admin has to spent lot of time to recover the server because the system admin cannot even get into single user mode due to the fact that file system has issues and the root password...

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RPM Package Management a Quick How To

Quick How to on Red Hat Package Manager (RPM) How to install packages with all the dependency packages if all the packages are available at a common repository? Ans : rpm -ivh --aid packagename.How to check, where a particular package installed it’s configuration files.Ans : rpm -qc packagename.How to check the change log of the installed package.Ans : rpm -q --changelog packagename.How to check, where a particular package installed it’s doc files.Ans : rpm -qd packagenmeHow to check all the files installed by package?Ans : rpm -q --filesbypkg...

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Enabling HTTPS Support in JBOSS

Perform the below steps to enable HTTPS support in JBOSS : 1. Execute the following command to generate encryption key for HTTPS. /usr/java/jdk1.5.0_14/bin/keytool -genkey -keyalg RSA -keystore jboss.keystore -validity 3650 2. The command will ask you some information like, name company, country etc. Provide the information, keystore password and key password for mykey. The command will create a file with name jboss.keystore in your current working directory. 3. Copy the keystore file to $JBOSS_HOME/server/all/conf/ folder. 4....

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Reserved Blocks in Linux

Reserved blocks are disk blocks reserved by the kernel for processes owned by privileged users to prevent operating system from a crash due to unavailability of storage space for critical processes.   For example, just imagine the size of root file system is 14 GB and the root file system is 100% full, all the non privileged user processes would not be able to write data to the root file system whereas processes which are owned by  privileged user (root by default) would still be able to write the data to the file system....

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Scanning SCSI Bus and HBA Devices in Linux

How to scan HBA’s to acquire newly added storage: Loop Initialization Protocol (issue_lip): Loop Initialization Protocol is a method to perform bus reset which scan the scsi bus and updates the scsi layer to reflect all the scsi devices. This is a asynchronous operation and may take longer time to complete. Usually after executing the command to trigger issue_lip, you would get a command prompt immediately, but in actual it might take up longer time to complete the bus scan. Loop Initialization Protocol method to scan the HBA’s can cause...

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Killing Multiple Processes

I was working on one of the issue today, where in the passwordless ssh was not working for one user.  When I checked, I found more than 3000 defunct processes running on the server owned by a specific user and the system was not allowing to start a new process due to the user's nproc limit. The same user was also running 100's of other processes which were not defunct.  The server was running multiple applications so I didn't had the liberty to reboot the server. Hence, the only option I had was to kill  all the processes which...

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sort: open failed: +1: No such file or directory

Newer versions of POSIX are not fully compatible with older version of POSIX as a result, there are some changes in the parameters/switches for some commands like sort. For Example, if the POSIX Version is 200112 or above, “sort +2″ command would through an error message “sort: open failed: +1: No such file or directory” as the newer version 200112 (1003.1-2001) is not fully compatible with POSIX older versions like 199209 (1003.2-1992). [root@vcsnode1 ~]# ps -ef | sort +2 sort: open failed: +2: No such file or directory [root@vcsnode1...

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