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
CentOS/RHEL 8: “ACPI MEMORY OR I/O RESET_REG” Server Hung after reboot
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
Process are stuck in D-state due to multipathd
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 the queue will fail all stored IOs. If the outage will last, the admin might wish to unplug the queues right-away. The following … [Read more...] about Process are stuck in D-state due to multipathd
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 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
“Preauthentication Failed While Getting Initial Credentials” – Kerberos Error
The Problem Not able to log into Kerberos using the keytab file. When trying to use the keytab file to log in, the following error is seen: Command: kinit -k -V -t [name].keytab HTTP/[PrincipalName] Error: kinit: preauthentication failed while getting initial credentials The Solution The error, "Preauthentication failed while getting initial credentials" happens when the password is incorrect. Update the keytab file on the problematic Kerberos client with the key provided from … [Read more...] about “Preauthentication Failed While Getting Initial Credentials” – Kerberos Error
“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