The Problem Rebooting the CentOS/RHEL 8 server causes it to freeze. From the console output, the system is stuck at: ... [ 68.906159] dracut: Disassembling device-mapper devices Rebooting. [ 68.934073] kvm: exiting hardware virtualization [ 68.936622] sd 0:0:0:0: [sda] Synchronizing SCSI cache [ 68.938942] e100e: EEE TX LPI TIMER: 00000011 [ 69.018502] reboot: Restarting system [ 69.020000] reboot: machine restart After removing "rhgb quiet" and adding "debug rd.debug" in grub … [Read more...] about CentOS/RHEL 8: “ACPI MEMORY OR I/O RESET_REG” Server Hung after reboot
Linux
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 and disable the rsh service to not start after reboot: # chkconfig rsh off Above command eg chkconfig does not stop rsh but … [Read more...] about How to Disable RSH Server in CentOS/RHEL
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 the file could be old one. NFS Clients caches various NFS data. RFC 1813 for NFSv3 specification says: Clients can perform caching in varied manner. and also says: The NFS version 3 … [Read more...] about How to disable NFS client caching in CentOS/RHEL
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 slower than reading from RAM, accessing memory pages there will result in a delay. The cache in Linux is used to speed up reads from disc - content which has been read once from disc is kept in … [Read more...] about How to disable swap in Linux
“Device /dev/mappper/mpath25 Not Found (or Ignored By Filtering)” – error while creating physical volume with pvcreate
The Problem When trying to create physical volume , getting the below error error: # pvcreate /dev/mappper/mpath25 Device /dev/mappper/mpath25 not found (or ignored by filtering). The issue can be reproduced at will with the following step: # pvcreate /dev/mappper/mpath25 The Solution Upon checking it was found that start sector was not zeroed out. # pvcreate /dev/mappper/mpath25 Device /dev/mappper/mpath25 not found (or ignored by filtering). # fdisk -l … [Read more...] about “Device /dev/mappper/mpath25 Not Found (or Ignored By Filtering)” – error while creating physical volume with pvcreate
“Read-only locking type set. Write locks are prohibited. Can’t get lock for [volume group]” – error during lvextend
The Problem Unable to extend LVM filesystem. The following error message is received on running the lvextend command: Read-only locking type set. Write locks are prohibited. Can't get lock for rootvg resize2fs 1.43-WIP (20-Jun-2013) The filesystem is already 1310720 blocks long. Nothing to do! The Solution The parameter locking_type is set to 4 in /etc/lvm/lvm.conf. # grep locking lvm.conf |grep -v '#' "lvmetad", "metadata", "cache", "locking" ] locking_type = 4 … [Read more...] about “Read-only locking type set. Write locks are prohibited. Can’t get lock for [volume group]” – error during lvextend
“error while loading shared libraries: libjli.so: cannot open shared object file: No such file or directory” ‘java -version’ error on Startup
The Problem "java -version" quits with the error message "error while loading shared libraries: libjli.so: cannot open shared object file: No such file or directory" when trying to start the JVM. Case 1 The problem is there if it is run under a normal user or if it is run under the root user $ java -version [PATH_TO]/java: error while loading shared libraries: libjli.so: cannot open shared object file: No such file or directory Case 2 The problem is there only if it is run by a normal … [Read more...] about “error while loading shared libraries: libjli.so: cannot open shared object file: No such file or directory” ‘java -version’ error on Startup
“java” command does not run the JVM that has been installed
The Problem A JDK/JRE from Oracle has been installed on a Linux machine according to the installation instructions. The "java" command does not run the JVM that has been installed. Java applications can fail to run if an unexpected Java Runtime Environment is found. Example from a Red Hat server: $ java -version java version "1.6.0_17" OpenJDK Runtime Environment (IcedTea6 1.7.4) (rhel-1.21.b17.el6-x86_64) OpenJDK 64-Bit Server VM (build 14.0-b16, mixed mode) Disclaimer: The … [Read more...] about “java” command does not run the JVM that has been installed
Windows Active Directory Account Shows Inconsistent UID/GID In Different Linux SSSD Clients (CentOS/RHEL)
The Problem The id command shows different UID and GID on different sssd servers for the same Windows Active Directory user. After purging the sssd cache by sss_cache, the UID and GID are still different. 1. Output from one server: # id ad_test_user uid=[UID](ad_test_user) gid=[GID](ad_test_group) groups=[GID](ad_test_group2),[GID](ad_test_group) # sss_cache -u ad_test_user # id ad_test_user uid=[UID](ad_test_user) gid=[GID](ad_test_group) … [Read more...] about Windows Active Directory Account Shows Inconsistent UID/GID In Different Linux SSSD Clients (CentOS/RHEL)
User Environment Variables With “su” and “sudo” in Linux
su and sudo allow to execute commands or shell with a different user. Depending on how they are invoked the environment variables can change, causing different command results. Both "su" and "sudo" allow to execute commands on behalf of other user. The usage of su implies the knowledge of the "other" user password except if invoked by root. There is not much control on what the user can do, if the access is granted there is no restriction. In sudo there is a fine control on what the user … [Read more...] about User Environment Variables With “su” and “sudo” in Linux