The Problem After a reboot the system will not start or activate one of the LVM volume groups. Trying to activate the group manually produces the message: Couldn’t find device with uuid ‘[UUID]’ The Solution The string LABELONE at the metadata location marks the device as being part of an LVM device. Without this string, […]
CentOS/RHEL
How To Check Current Values for Kernel Tuning Parameters in CentOS/RHEL
Question: How to check to current values for these kernel parameters? net.core.netdev_max_backlog fs.file-max net.ipv4.tcp_max_syn_backlog net.core.somaxconn The linux system could not support to method for directly check these values but we can check to using by below commands : # netstat -an | grep -c SYN_RECV # netstat -s Also, those parameter can be checked from […]
How to calculate recommended value of vm.min_free_kbytes Kernel Tuning Parameter
/proc/sys/vm/min_free_kbytes: This controls the amount of memory that is kept free for use by special reserves including “atomic” allocations (those which cannot wait for reclaim). Setting vm.min_free_kbytes too low prevents the system from reclaiming memory. This can result in system hangs and OOM-killing multiple processes. However, setting this parameter to a value that is too […]
how to rotate Tang Server Keys and update the Clevis Client
This post explains how to rotate Tang Server Keys and update the Clevis Client. Note, below is an example hence all certificates, keys and device names/uuid’s are fictional. Change the keys on the tang server 1. Check existing key: # ls -la /var/db/tang total 8 dr-xrws—. 2 tang tang 84 Jun 26 11:24 . drwxr-xr-x. […]
Disk Encryption Using Network Based Key Services (NBDE) on CentOS/RHEL 8
Question: How to create an encrypted XFS filesystem that’s automatically unlocked at boot using clevis (client) and tang (server)? Red Hat has included disk encryption for years with Linux Unified Key Setup-on-disk-format (LUKS). This solution is easy to implement and configure for your encryption needs, but the management and practicality of its key management is […]
“Volume “myvg/vol01″ Is Not Active Locally” – CentOS/RHEL
The Problem While trying to create a logical volume, lvcreate fails with error “Volume “myvg/vol01″ Is Not Active Locally” even though the volume group is active, with an error output such as the following: [root@ ~]# lvcreate -L 4G myvg Volume “myvg/vol01” is not active locally. Aborting. Failed to wipe start of new LV. The […]
“Authorization not available. Check if polkit service is running or see debug message for more information” – CentOS/RHEL 7 ssh service error
The Problem Starting ssh services errors out and spool messages regarding polkit service. # service sshd restart Redirecting to /bin/systemctl restart sshd.service Authorization not available. Check if polkit service is running or see debug message for more information. Same issue is encountered when starting the polkit service. # service polkit restart Redirecting to /bin/systemctl restart […]
How to Configure Network Interface Teaming in CentOS/RHEL 7 and 8
Network interface teaming was introduced from CentOS/RHEL 7 as a more extensible and scalable alternative to network bonding. This post describes how to configure network teaming on CentOS/RHEL 7/8. The examples provided are based on Oracle Linux 8.2 system (Oracle VirtualBox 6.1 guest virtual machine) with two network interfaces using NetworkManager. Specifically, the Network Manager […]
“VFS: Cannot open root device “UUID=[UUID]” or unknown-block(0,0)” – Booting issue CentOS/RHEL/OEL 6
The Problem Server fails to boot with latest kernel with the below errors from console logs: Initializing network drop monitor service md: Waiting for all devices to be available before autodetect md: If you don’t use raid, use raid=noautodetect md: Autodetecting RAID arrays. md: Scanned 0 and added 0 devices. md: autorun … md: … […]
How to Find the Original Installation OS Version in CentOS/RHEL
This post explains how to find the OS version which was first installed on a CentOS/RHEL system. CentOS/RHEL 6 Run grep -m1 “label =” /var/log/anaconda.storage.log to find the original installation OS version. Current version: # cat /etc/redhat-release CentOS Linux release 6.10 Original installation version: # grep -m1 “label =” /var/log/anaconda.storage.log label = EL6.8_x86_64_Disc_1_20160518 size = […]