The Error While trying to boot grub2 shows: error: can’t find command ‘ffffffffff….. and the system is unable to boot. The Solution It is possible that the grub2 modules in /boot/grub2/fonts/ /boot/grub2/i386-pc/ /boot/grub2/locale/ have become corrupted. To remedy any bootloader corruption, boot the server into rescue mode and reinstall the grub2 package: 1. Boot the […]
CentOS/RHEL 7
rpc.statd[PID]: Failed to create listener xprt (statd, 1, udp6) – CentOS/RHEL 6, 7
The Problem rpc.statd(or rpc.*) logs following error messages into syslog(/var/log/messages): Nov 29 11:01:34 hostname rpc.statd[12345]: Failed to create listener xprt (statd, 1, udp6) Nov 29 11:01:34 hostname rpc.statd[12345]: Failed to create listener xprt (statd, 1, tcp6) Or you can also check the rpc-statd.service status: # systemctl status rpc-statd.service ● rpc-statd.service – NFS status monitor for […]
How to enable Debug Option For CIFS Module in CentOS/RHEL 7 and 8
Question: How to configure CIFS debug option in Linux servers to provide additional debug information in the client system logs? 1. Take backup of existing debug or to check the default value: # cp /sys/kernel/debug/dynamic_debug/control /root/backup # cat /proc/fs/cifs/cifsFYI # cat /proc/fs/cifs/traceSMB 2. Enable debug chosen options: # echo ‘module cifs +p’ > /sys/kernel/debug/dynamic_debug/control # […]
How to Debug systemd boot process in CentOS/RHEL 7 and 8
Question: How to debug/find, changes or failing commands during boot process? During boot process, when seeing grub boot menu press “e” for edit the grub, then scroll down until you see boot entry: echo “Loading Linux… linux16 /vmlinuz-XXX root=XXXro crashkernel=auto rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet LANG=en_US.UTF-8 On the line with “linux” remove the following entries if […]
“not enough to start the array” – error while staring mdadm RAID array
The Problem After replacing issue disk on software RAID, mdadm Fails to Start the RAID Array with Error – “not enough to start the array” and Software Raid State is showing “active, FAILED, Not Started” “mdadm –detail /dev/md0” showing only 4 disks are active and 8 removed disks. # mdadm –detail /dev/md0 State : active, […]
“Logical volume vg/lv contains a filesystem in use” – while removing LVM filesystem
The Problem How to remove an LVM volume which returns “filesystem in use” error. # lvchange -an /dev/mapper/vg-lv Logical volume vg/lv contains a filesystem in use The Solution Step 1: Try to identify if this particular LVM is mounted in your server. # mount -a | grep /path-to-LV-volume If mounted, unmount it. Step 2: Check […]
How to disable ACPI in CentOS/RHEL 7
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 […]
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: # […]
“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 […]
“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 […]