CentOS/RHEL 6

The Problem lvdisplay command prints the below error on a CentOS/RHEL 6 system: # lvdisplay Failed to create directory /var/lock/lvm File-based locking initilisation failed. The Solution The above error is due to the /var file system is mounted as read only. To resolve the issue, follow the steps outlined below: 1. Edit and modify /etc/lvm/lvm.conf as below: locking_dir = "/var/lock/lvm" to locking_dir = "/tmp/lock/lvm" 2. Run the lvm commands by defining temporary locking … [Read more...] about lvdisplay error: “Failed to create directory /var/lock/lvm. File-based locking initilisation failed.”

The Problem The server continuously displaying below messages in /var/log/messages or dmesg log file: avahi-daemon[23373]: server.c: Packet too short or invalid while reading response record. (Maybe an UTF8 problem?) The Solution This is avahi-daemon issue related to network environment. The avahi-daemon is application for zeroconf implementation. The avahi-daemon working related of to DNS(mDSN). The avahi-daemon approaching and searching to each other user or devices for local network … [Read more...] about The System Continuously Displayed the Error Message from the “avahi-demon” in /var/log/messages

This post explains how to configure 'autofs' in order to mount NFS file systems with 'autofs' service. 1. Stop 'autofs' service, check if the service is running then proceed to stop it. # service autofs status automount (pid 25285) is running... # service autofs stop Stopping automount: [ OK ] # service autofs status automount is stopped 2. Edit the /etc/auto.master file to set the file map: The file /etc/auto.master is the main configuration file for 'autofs' service, this file … [Read more...] about How to Mount NFS File Systems Using ‘autofs’ in CentOS/RHEL

For CentOS/RHEL 5 and 6 On CentOS/RHEL 5 there is no configuration file for snmptrapd.conf. As per manual pages "The Net-SNMP notification receiver (trap daemon) uses one or more configuration files to control its operation and how incoming traps(and INFORM requests) should be processed. This file (snmptrapd.conf)can be located in one of several locations, as described in the snmp_config(5) manual page." The configuration file /etc/snmp/snmptrapd.conf can be manually created if it doesn't … [Read more...] about How To Configure SNMP Daemons: snmpd and snmptrapd on CentOS/RHEL 5,6 and 7

The post is to illustrate the steps to configure the smtp relay using postfix on CentOS/RHEL 5 and 6. For relaying mail through another smtp server, /etc/postfix/main.cf file has to be configured with "relayhost" parameter which specifies the destination smtp server. 1. Install the postfix rpm if not installed already. # rpm -qa|grep postfix 2. Take a backup of the default configuration: # cp /etc/postfix/main.cf /etc/postfix/main.cf.bkp_default 3. Edit the /etc/postfix/main.cf … [Read more...] about How to configure postifx smtp relay in CentOS/RHEL 5 and 6

The post explains how kernel semaphore limits can be changed in a CentOS/RHEL server. Kernel Parameters to set semaphore limits The kernel parameters to set the semaphore limits are: kernel.sem = SEMMSL SEMMNS SEMOPM SEMMNI SEMMSL - max semaphores per array SEMMNS - max semaphores system wide SEMOPM - max ops per semop call SEMMNI - max number of arrays Changing Semaphore Limits If a limit needs to be changed there should be taken in to account that (max number of arrays)*(max … [Read more...] about How to Change Kernel Semaphore Limits in CentOS/RHEL

Question: How to Enable or disable HBA ports temporarily, without a reboot? 1. Locate the HBA address on the PCI bus: # lspci -k ... 19:00.0 Fibre Channel: QLogic Corp. ISP2532-based 8Gb Fibre Channel to PCI Express HBA (rev 02) Subsystem: QLogic Corp. Device 0171 Kernel driver in use: qla2xxx 19:00.1 Fibre Channel: QLogic Corp. ISP2532-based 8Gb Fibre Channel to PCI Express HBA (rev 02) Subsystem: QLogic Corp. Device 0171 Kernel driver in use: … [Read more...] about How to disable or enable an HBA without reboot under CentOS/RHEL

The Problem Log into vsftp server with anonymous user from ftp client, try to upload a file fails with error message: # ftp vsftpsrv Connected to vsftpsrv (10.182.38.176). 220 (vsFTPd 2.0.5) Name (10.182.38.176:root): anonymous 331 Please specify the password. Password: 230 Login successful. Remote system type is UNIX. Using binary mode to transfer files. ftp> pwd 257 "/" ftp> ls 227 Entering Passive Mode (10,182,38,176,29,34) 150 Here comes the directory listing. drwxr-xr-x 2 … [Read more...] about Anonymous User Fails to Upload File to VSFTP Server

Question: A user would like to restrict the ssh login access to a server by a specific user and/or by client ip address. How this can be achieved? Note: The configuration may differ between Oracle Linux 6 and 7 due to differences in the versions of OpenSSH bundled with each operating system. CentOS/RHEL 7 allows "nested" configuration in /etc/ssh/sshd_config. The following is an example: # vi /etc/ssh/sshd_config Match User testuser AllowUsers *@192.168.1.x However, in CentOS/RHEL 6, … [Read more...] about How to restrict ssh logins by user and client address on CentOS/RHEL

The Problem After system has booted md0 is missing and all LVs used on top of md0 are not mounted # mount -a mount: special device /dev/mapper/vg_test-x0 does not exist mount: special device /dev/mapper/vg_test-y0 does not exist # cat /etc/mdadm.conf ARRAY /dev/md0 level=raid5 num-devices=6 metadata=0.90 spares=1 UUID=73560e25:92fb30cb:1c74ff07:ca1df0f7 # cat /proc/mdstat Personalities : unused devices: [none] More data to show that /dev/md0 is missing: # mdadm --detail … [Read more...] about “mdadm: No arrays found in config file” – error on running ‘mdadm –assemble –scan’