Archives for June 2017

If you use vim text editor, you would have seen the colorful text mark-up. It helps a lot in case you are writing scripts. By default vi editor does not have this feature enabled. Follow the steps below to enable the text colour feature in vi. 1. install vim-enhanced if not already installed. # yum install vim-enhanced 2. Hash out the line containing "[ -n "$ID" -a "$ID" -le 200 ] && return". # vi /etc/profile.d/vim.sh if [ -n "$BASH_VERSION" -o -n "$KSH_VERSION" -o -n … [Read more...] about How to enable text colour in vi similar to vim in CentOS/RHEL

We can use the rpcdebug command to set and clear the Linux kernel's NFS client and server debug flags. Setting these flags causes the kernel to log messages to the system log ( in response to NFS activity. Below is a list of modules which for which kernel debug flags can be set using rpcdebug command. ModuleFunction nfsNFS client nfsdNFS server nlmNetwork Lock Manager Protocol(NLM) rpcRemote Procedure Call Viewing available rpcdebug modules 1. To view available rpcdebug … [Read more...] about How to enable NFS debug logging using rpcdebug

Metadata backups and archives are automatically created on every volume group and logical volume configuration change unless disabled in the /etc/lvm/lvm.conf file. By default, the metadata backup is stored in the /etc/lvm/backup directory. Each Volume group backup is stored in this directory with file name same as the VG name. The metadata archives are stored in the /etc/lvm/archive directory. How long the the metadata archives stored in the /etc/lvm/archive directory are kept and how many … [Read more...] about CentOS / RHEL : How to find the creation time of LVM volume

While deleting a LUKS encrypted device using lvremove you would get an error as below : # lvremove /dev/mapper/datavg-lv_cryptvol Logical volume datavg/lv_cryptvol is used by another device. The reason being - it is a LUKS encrypted volume. Follow the steps below to delete a LUKS encrypted device. Deleting LUKS volume 1. Determining the underlying device Run the following command to determine the underlying device for the LUKS device: # cryptsetup status … [Read more...] about CentOS / RHEL : How to delete LUKS encrypted device

Special Permissions - SUID/SGID There are two special permissions that can be set on executable files: Set User ID (setuid) and Set Group ID (sgid). These permissions allow the file being executed to be executed with the privileges of the owner or the group. For example, if a file was owned by the root user and has the setuid bit set, no matter who executed the file it would always run with root user privileges. Finding files with SUID/SGID bit set We can find all the files with SUID SGID … [Read more...] about Linux / UNIX : How to find files which has SUID/SGID set

Control groups (strong>cgroups) enable you to allocate computing resources to specific processes or tasks. You can assign a set of CPU and memory to a specific group of tasks or even to a specific user. The post here details out the steps to allocate a defined memory resource to a specific use. Ulimit won't be able to achieve this goal as ulimit limits user memory consumption per process. The best possible option is to use cgroups. With cgroups users can be limited not only to meomry resources … [Read more...] about CentOS / RHEL 6 : How to limit memory resources for a specific user using cgroups