Oracle Linux

Question: How to change timezone in CentOS/RHEL 7 server from EST to CST. Follow the below steps to change the timezone to CST. (Execute the below commands as root user) 1. List all the available timezones using the below command: # timedatectl list-timezones 2. Locate the correct timezone you need that is in the central timezone. 3. Set the specific timezone. For example, to set central timezone: # timedatectl set-timezone America/Chicago 4. Run the "date" command to verify the … [Read more...] about How to Change Timezone from CST To EST in CentOS/RHEL 7 Server

Question: How to change the password policy on a system so that a user cannot choose any of the last 3 passwords previously used? 1. Make sure that the file /etc/security/opasswd has the default permission (600). # ls -l /etc/security/opasswd -rw------- 1 root root 116 Sep 8 14:52 /etc/security/opasswd 2. Ensure you backup the file /etc/pam.d/system-auth: # cp /etc/pam.d/system-auth /etc/pam.d/system-auth.old 3. Modify the file /etc/pam.d/system-auth in vi editor and change the line … [Read more...] about How to configure CentOS/RHEL 6 system to not used last 3 passwords used

The Problem Some user directories cannot be deleted. For example: /root/.cache/doc/ directory /root/.cache/doc/by-app directory If we try to delete the directory, we get the below error: # rm -rf /root/.cache/doc/ rm: cannot remove 'doc/by-app': Function not implemented The Solution The directories are the mount points for /dev/fuse device. # mount --mount (ext, ocfs2, nfs, gfs, fuse, cifs, btrfs, xfs) /dev/fuse on /root/.cache/doc type fuse … [Read more...] about rm: cannot remove ‘doc/by-app’: Function not implemented (CentOS/RHEL 7)

The Problem Trying to login via SSH, the session hangs. Adding "-vvv" option, shows that it hangs with below messages: debug1: expecting SSH2_MSG_KEX_ECDH_REPLY The Solution MTU was set to 9000 : # ip add| grep -i eth0 2: eth0: mtu 9000 qdisc pfifo_fast state UP group default qlen 1000 inet x.x.x.x/24 brd x.x.x.x scope global noprefixroute eth0 Tcpdump captured for both nodes shows that a packet whose length is greater than 1500 was being retransmitted. 5 11:13:10.261757 x.x.x.x … [Read more...] about SSH Login Stuck At : “debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP” CentOS/RHEL 7

The Problem Under /etc/systemd/system the mount unit file was created with name "test.mount". The mount point directory created is /home/test. Under the mount unit file options in the "Where=" the mount point configured is /home/test. The device where the filesystem will be mounted is /dev/xvdb1 and it was defined under "What=" option. When configuring mount unit file to mount a filesystem, it fails with the following error: # systemctl start test.mount Failed to start test.mount: Unit is not … [Read more...] about “Failed to start test.mount: Unit is not loaded properly: Invalid argument.” – While mounting a fileystem using systemd

Disabling lvm2-lvmetad.socket/service on CentOS/RHEL 7 system works while the system is running, but after a reboot, it comes up again. This post will show you how to prevent this from happening. 1. Modify the /etc/lvm/lvm.conf file with your favorite file editor, like vi or nano, and switch the value of "use_lvmetad = " from 1 to 0. # vi /etc/lvm/lvm.conf use_lvmetad = 0 2. Stop, Disable, and Mask the lvm2-lvmetad service/socket. # systemctl stop lvm2-lvmetad.service … [Read more...] about How to Disable the ‘lvm2-lvmetad.socket/service’ on CentOS/RHEL 7

The scope of this post is to explain the steps involved in increasing the /boot filesystem, when no sufficient space available to install new kernel package. Though we have standard methods to reduce the size of /boot i.e. removing unused kernel and image files from boot, as an alternate approach, this post illustrate the steps to expand size of boot partition. The following should be the scenario were this can be applied, OVM/Vmware guest machine. Guest Backup should be taken from … [Read more...] about Extend the size of /boot partition on virtualized environment (CentOS/RHEL 6)

On a CentOS/RHEL 7, the network interface will be named like enoxxx. This post provides steps on how to disable such "Predictable Network Interface Device Names". We can use the following ways to disable the predictable network interfaces: 1. Create your own manual naming scheme by defining your own udev rules file in /etc/udev/rules.d folder and set the NAME property for the devices. Make sure to order it before the default policy file which is … [Read more...] about How to Disable “Predictable Network Interface Device Names” in CentOS/RHEL 7

Question: How to create a 3 mirror RAID1 "md" device by adding a 3rd disk to a 2 mirror device? # cat /proc/mdstat Personalities : [raid1] md123 : active raid1 sda4[0] sdb4[1] 204736 blocks super 1.0 [2/2] [UU] bitmap: 0/1 pages [0KB], 65536KB chunk md124 : active raid1 sda1[0] sdb1[1] 524906496 blocks super 1.2 [2/2] [UU] bitmap: 0/4 pages [0KB], 65536KB chunk md125 : active raid1 sda2[0] sdb2[1] 2099200 blocks super 1.2 [2/2] [UU] md126 : active raid1 sda3[0] … [Read more...] about How to Add a 3rd Disk to Create a 3-way Mirror RAID1 MD Device (CentOS/RHEL 7)