For multipaths with queueing enabled and with all paths down, the kernel will store submitted IOs in a queue and resubmit them upon path recovery. Process submitting IOs to these multipath are stuck in D-state (uninterruptible sleep). The ‘no_path_retry 4‘ multipath parameter will instruct the kernel to unplug the queue after 4 failed path-tests. Unplugging […]
Archives for March 2021
How to Disable RSH Server in CentOS/RHEL
Question: How to completely disable RSH Server, and if necessary, uninstall it? To disable rsh-server: 1. Verify if rsh-server package is installed: # rpm -qa | grep rsh-server 2. If above command will return rsh-server package follow below action plan: # vi /etc/xinetd.d/rlogin specify there: disable = yes 3. Remove rsh entry from /etc/securetty file […]
How to disable NFS client caching in CentOS/RHEL
Occasionally the NFS Client does not read data from NFS exports synchronously, such as when it was written by another NFS Client. For example, after NFS Client A writes a file by “echo hello > /NFS_mountpoint/testfile”, NFS Client B can not read the file with “No such file”, or can read but the contents of […]
How to Hot-add and Remove Logical Memory in CentOS/RHEL 7
This post explains how to use memory hotplug to increase/decrease the amount of memory. To see (online/offline) state of memory section, read ‘state’ file. # grep line /sys/devices/system/memory/*/state /sys/devices/system/memory/memory0/state:online /sys/devices/system/memory/memory1/state:online /sys/devices/system/memory/memory2/state:online /sys/devices/system/memory/memory3/state:online /sys/devices/system/memory/memory4/state:online To set a memory[x] to online/offline: # echo online > /sys/devices/system/memory/memory[number]/state # echo offline > /sys/devices/system/memory/memory[number]/state To verify the current state: # […]
How to disable swap in Linux
Besides the RAM there is a so-called Swap, which is a virtual memory, where RAM content (pages) could be swapped-in in case there is not enough RAM available anymore. It could be a disk partition, Logical volume, or even a file. This swap is located on the disc and since disc reads and writes are […]