Question: How to send emails to external users with mailx running on CentOS/RHEL system? The following command shows how to send a mail to an external user using mailx: # echo “this is the body of the email” | mailx -vvv -s “test mail” -r “From” -S smtp=”your-smtp” someone@address Here, -vvv = Verbosity. -s = […]
Archives for June 2019
How to Replace a Failed Btrfs Device
The Problem Originally the btrfs file system is build on multiple disks. # btrfs filesystem show Label: ‘MYBTRFS’ uuid: 09138ad8-eb2f-4c7c-aef7-90482a67c45c Total devices 3 FS bytes used 768.00KiB devid 1 size 5.00GiB used 1.52GiB path /dev/xvdb devid 2 size 5.00GiB used 520.00MiB path /dev/xvdc devid 3 size 5.00GiB used 1.51GiB path /dev/xvdd For some reason one […]
How to Check Btrfs FileSystem Usage and Perform Balancing
In Btrfs file system there are chunks that are allocated for regular data, metadata. There are also chunks that are allocated to store file system information and also about where other chunks are located on the physical disk. Those chunks can only store the data. Very occasionally, a chunk type may fill up and start […]
How to Re-Balance BTRFS to Free Disk Space
The Problem The BTRFS filesystem has filled on the server, and thus some space needs to be freed up on it. There is a re-balancing feature available in btrfs. The primary purpose of the re-balance feature is to spread block groups across all devices so they match constraints defined by the respective profiles and this […]
How To Change Pacemaker Cluster Heartbeat Timeout In CentOS/RHEL 7
Question: How to change pacemaker cluster heartbeat timeout in CentOS/RHEL 7? By default, the heartbeat of pacemaker in CentOS/RHEL 7 is set to 1000(ms), you could increase it by the below steps. 1. Appending/Chaning the token to the totem section in the corosync config file /etc/corosync/corosync.conf. # cat /etc/corosync/corosync.conf totem { version: 2 cluster_name: pcmk […]
Understanding OS load average and run queue/blocked queue in terms of CPU utilization in Linux
When it comes to troubleshooting a performance issue on Linux, it is very important to know the basics of various command outputs such as uptime, vmstat. In this post, we will try to understand the load averages and run queue/blocked queue in terms of CPU utilization. First, let’s understand what is Load Average: Load average […]
“docker dead but subsys locked” – error while starting docker
The Problem The docker engine package was upgraded. After that the user is not able to start the docker service, and revert back with error “docker dead but subsys locked” on verifying the status of the service. Under normal circumstances, the general solution would be to remove the lock file and the dead files of […]
How to Change Password Of An LXC Container User Account
An LXC container has its own username and password definitions. The password for an LXC account can be changed when needed, whether or not the container is running. geeklab login: admin Password: Login incorrect Oracle Linux Server 7.1 Kernel 3.8.13-118.19.3.el6uek.x86_64 on an x86_64 Resetting forgotten LXC container user password Connect To A Running Container As […]