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 […]
CentOS/RHEL 6
“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 […]
“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. […]
“WARNING: Failed to connect to lvmetad. Falling back to device scanning” – error while running LVM commands
The Problem The LVM commands showing below errors: # pvs WARNING: Failed to connect to lvmetad. Falling back to device scanning. >>>> Masked Active: inactive (dead) Sep 08 20:34:29 systemd[1]: Cannot add dependency job for unit lvm2-lvmetad.socket, ignoring: Unit is masked. Sep 08 20:34:32 systemd[1]: Cannot add dependency job for unit lvm2-lvmetad.socket, ignoring: Invalid request […]
CentOS/RHEL: “id” command doesn’t list the Group Name against GID for LDAP Users
The Problem While running “id” command against LDAP users, it only displays the gid for some secondary group and the group name is not being printed: # id user1 uid=48254(user1) gid=100(users) groups=100(users),5002(group1),5001(group2),41257(group3),856(group4),56971 And, the below error was logged in /var/log/sssd/sssd_nss.log : (Tue Mar 14 05:40:09 2020) [sssd[nss]] [nss_cmd_getgrgid_search] (0x0010): getgrgid call returned more than one […]
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) […]
How To Generate An CentOS/RHEL 6 UEFI Bootable ISO Image
1. Mount CentOS/RHEL 6.9 installation iso into /media/RHEL6.9; # mkdir /media/RHEL6.9 # mount -o ro /dev/cdrom /media/RHEL6.9 2. Create a new folder /opt/make_iso; # mkdir /opt/make_iso 3. Copy all files of CentOS/RHEL 6.9 installation iso to /opt/make_iso; # tar cf – /media/RHEL6.9 | ( cd /opt/make_iso/; tar xpvf – ) 4. Copy uefi kickstart config […]
How to Update the hostname in Shell Prompt Once it is Changed in the Linux OS
Question: In this case, the hostname(geeklab) has already been updated in /etc/sysconfig/network and /etc/hosts file, but still needs to be updated in the shell prompt. For example, to change the old shell prompt as below: From : [root@geek ~]# To : [root@geeklab ~]# OS: CentOS/RHEL 6 and 7 Changing the Shell Prompt On the fly […]
How to Configure NFS Services (server-side) to Run on Static Ports as an Alternative CentOS/RHEL 5 and 6
By default, some NFS services (server_side) use well-known ports but some normally just use random ports. The use of random ports does not work so well with strict firewall rules blocking random yet unknown ports. So, sometimes it is best to manually alter or specify static ports for NFS services (server_side) to use. This post […]
How to blacklist a local disk using the “find_multipaths” directive in CentOS/RHEL 6
After a system reboot, locally attached disks (eg /dev/sda1) are assigned device mapper multipath (“dm-multipath”, “dm-mp”) names (e.g. /dev/mapper/mpath1p1). Any SCSI device for that matter, which has a scsi ID and is not OPEN/mounted, will be assigned by dm-multipath during boot process unless blacklisted in multipath configuration. Follow the stpes outlined below in order to […]