ACPI stands for Advanced Configuration and Power Interface. It is the system that controls hardware actions such as the dynamic speed fans, the power button behavior, system sleep states, and helps to identify some system capabilities. ACPI power-saving features are hierarchical, meaning that any device running “behind” another will be dependent on the power state of the parent device. For example, a device cannot be running in full power “behind” a device that is sleeping or in standby … [Read more...] about How to disable ACPI in CentOS/RHEL 7
CentOS/RHEL 7
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 … [Read more...] about How to Hot-add and Remove Logical Memory in CentOS/RHEL 7
“Connection reset by peer” – error while ssh into a CentOS/RHEL system with a specific user only
The Problem When trying to open an ssh connection to a system with a specific account, it failed with 'Connection reset by peer'. Other users can successfully connect with ssh to this system. Below is an example showing the failed login to node [NODE2] with the account 'oracle'. [oracle@NODE1]$ ssh oracle@[NODE2] oracle@[NODE2]'s password: Read from remote host [NODE2]: Connection reset by peer Connection to [NODE2] closed. [oracle@NODE1]$ ssh root@[NODE2] root@[NODE2]'s … [Read more...] about “Connection reset by peer” – error while ssh into a CentOS/RHEL system with a specific user only
“Couldn’t authenticate with keytab while discovering which salt to use: hostname: KDC has no support for encryption type” – error while joining domain
The Problem A CentOS/RHEL 6 client fails to be enrolled in an Active Directory domain, with the adcli command randomly failing with the following error written to the console: Couldn't authenticate with keytab while discovering which salt to use: [SERVER$@DOMAIN_NAME]: KDC has no support for encryption type The following errors are logged at the same time to /var/log/messages: Feb 20 16:23:52 [hostname] [sssd[ldap_child[27134]]]: Failed to initialize credentials using keytab … [Read more...] about “Couldn’t authenticate with keytab while discovering which salt to use: hostname: KDC has no support for encryption type” – error while joining domain
How to Switch Back To Previous Version of openjdk in CentOS/RHEL
Question: How to downgrade the Java version which got installed/updated during system patching? 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. Recent version is - java-1.8.0-openjdk-1.8.0.51-1.b16.el6_7.x86_64 Required version is - java-1.7.0-openjdk-1.7.0.85-2.6.1.3.0.1.el6_7.x86_64 # rpm -qa | grep -i openjdk java-1.8.0-openjdk-1.8.0.51-1.b16.el6_7.x86_64 … [Read more...] about How to Switch Back To Previous Version of openjdk in CentOS/RHEL
“systemd-udevd: Cannot Allocate Memory” and “A start job is running for dev-mapper-\x2droot.device” – CentOS/RHEL 7 booting issue
The Problem System cannot proceed with the boot process, stuck with an error messages: systemd-udevd[369]: fork of '/bin/sh -c '>/tmp/.lvm_scan-sdc;'' failed: Cannot allocate memory A start job is running for dev-mapper-\x2droot.device The Solution If the systemd unit called lvmetad is enabled and running, the metadata is cached which reduces disk scanning and it provides LVM commands with VG metadata and PV state. LVM commands will then avoid reading the information from disks. If there … [Read more...] about “systemd-udevd: Cannot Allocate Memory” and “A start job is running for dev-mapper-\x2droot.device” – CentOS/RHEL 7 booting issue
“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
“dracut-initqueue[286]: Warning: dracut initqueue timeout – starting timeout scripts” – CentOS/RHEL 7 booting issue
The Problem Messages "dracut-initqueue timeout - starting timeout scripts" are printed loop while booting then an Emergency shell is launched: dracut-initqueue[]: Warning: dracut initqueue timeout - starting timeout scripts dracut-initqueue[]: Warning: dracut initqueue timeout - starting timeout scripts dracut-initqueue[]: Warning: dracut initqueue timeout - starting timeout scripts dracut-initqueue[]: Warning: dracut initqueue timeout - starting timeout scripts dracut-initqueue[]: … [Read more...] about “dracut-initqueue[286]: Warning: dracut initqueue timeout – starting timeout scripts” – CentOS/RHEL 7 booting issue
“Failed to Start Activation of LVM2 Logical Volumes” and “Unit lvm2-activation-net.service Entered Failed State” – CentOS/RHEL 7 booting issue
The Problem System cannot boot-up properly with below logs: [ OK ] Started File System Check on /dev/xvdd. [ OK ] Started File System Check on /dev/xvdg. [ OK ] Started File System Check on /dev/xvdb. [ OK ] Started File System Check on /dev/xvdc. [ OK ] Started File System Check on /dev/disk/by-label/BOOT. Mounting /boot... [ OK ] Mounted /boot. [FAILED] Failed to start LVM2 PV scan on device 202:65. See 'systemctl status lvm2-pvscan@202:65.service' for details. [FAILED] Failed to … [Read more...] about “Failed to Start Activation of LVM2 Logical Volumes” and “Unit lvm2-activation-net.service Entered Failed State” – CentOS/RHEL 7 booting issue