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
CentOS/RHEL 5
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 describes how to configure NFS services (server-side) to run on static ports as an alternative. Overview NFS services (server-side) include: NLM (NFS lock … [Read more...] about How to Configure NFS Services (server-side) to Run on Static Ports as an Alternative CentOS/RHEL 5 and 6
FATAL: Error inserting rds_rdma
The Problem RDS module is not loading after rebooting the nodes of the cluster. Therefore, the CRS cannot run on any of the nodes. When trying to load the module the following errors are displayed: # modprobe rds_rdma FATAL: Error inserting rds_rdma /lib/modules/2.6.18-274.18.1.0.1.el5/updates/net/rds/rds_rdma.ko): Unknown symbol in module, or unknown parameter (see dmesg) dmesg output shows the following entries: rds_rdma: Unknown symbol rds_cong_map_updated rds_rdma: Unknown symbol … [Read more...] about FATAL: Error inserting rds_rdma
Failed to start LSB: Bring up/down networking – On restarting network service CentOS/RHEL (DHCP client)
The Problem Cannot reliably get networking to start on a server when using DHCP: # sudo /etc/init.d/network restart Restarting network (via systemctl): Job for network.service failed because the control process exited with error code. See "systemctl status network.service" and "journalctl -xe" for details. [FAILED] # journalctl -xe Nov 29 18:57:42 hostaname.domain.com dhclient[37653]: exiting. Nov 29 18:57:42 hostaname.domain.com network[37498]: [FAILED] Nov 29 18:57:42 … [Read more...] about Failed to start LSB: Bring up/down networking – On restarting network service CentOS/RHEL (DHCP client)
How to Capture More Logs in /var/log/dmesg for CentOS/RHEL
Sometimes not all log messages in /var/log/dmesg can be captured after Linux OS/kernel boots up because of too many block devices attached to the server. This post illustrates another way to record all bootup log messages besides configuring the serial console. Basically kernel parameter "log_buf_len" can be configured to increase kernel log buffer size, Name: log_buf_len, Set the size of the kernel log buffer. Synopsis: log_buf_len= n [ KMG ] Description: Set the size of the … [Read more...] about How to Capture More Logs in /var/log/dmesg for CentOS/RHEL
How to enable additional scsi logging in CentOS/RHEL
Question: How to turn on scsi extended debug messages? What are the field/flag definitions of scsi_logging_level? Additional scsi logging messages can be enabled by writing to /proc/sys/dev/scsi/logging_level either via use of the echo or preferably the sysctl command. The kernel parameter consists of ten packed fields, each 3 bits in length. Each field can have a value of 0 to 7. The higher the field's value, the more verbose the logging of messages associated with that field type. NOTE: … [Read more...] about How to enable additional scsi logging in CentOS/RHEL
How to Disable rpc.quotad Service in CentOS/RHEL 6 and 7
This post explains how to disable rpc.quotad service on CentOS/RHEL 6 or 7 machines. The protocol used by rpc.rquotad is an unsecured and obsolete protocol and should be disabled. Note: This procedure can disrupt NFS clients relying on disk quotas. To avoid issues, schedule a maintenance outage and stop these NFS clients. For CentOS/RHEL 6 or earlier 1. Edit the configuration file /etc/sysconfig/nfs to have an entry which reads RQUOTAD="no". For example: # grep RQUOTAD … [Read more...] about How to Disable rpc.quotad Service in CentOS/RHEL 6 and 7
How to configure Linux Resource Groups (cgroups) for MySQL
The following provides the procedure for configuring and using resource groups under Linux: 1. To use cgroups, you must install the "libcgroup" package on your system. # yum install libcgroup 2. Create a config file for cgroups (/etc/cgconfig.conf) and add below configuration. # vi /etc/cgconfig.conf mount { cpu = /cgroup/cpumem; cpuset = /cgroup/cpumem; memory = /cgroup/cpumem; } # High priority group group mysqldb { cpu { # Allocate the relative share of CPU resources … [Read more...] about How to configure Linux Resource Groups (cgroups) for MySQL
What are “segfault” messages in /var/log/messages file
This post explains how to analyse the segfault message in message file and to identify the problem in application or operating system side. What is "segfault"? A segmentation fault (often shortened to segfault) or access violation is a fault raised by hardware with memory protection, to notify operating system (OS) about a memory access violation. The Linux kernel will response it by performing some corrective action, generally passing the fault to the offending process by sending the … [Read more...] about What are “segfault” messages in /var/log/messages file
rpm: error while loading shared libraries: invalid ELF header
The Problem rpm commands issue the following error: rpm: error while loading shared libraries: /usr/lib64/liblzma.so.0: invalid ELF header The Solution In this instance, either liblzma.so or the link to it (/usr/lib64/liblzma.so.0) had gotten overwritten. $ rpm -qa | grep binutils rpm: error while loading shared libraries: /usr/lib64/liblzma.so.0: invalid ELF header To resolve this issue, the liblzma.so file and associated soft link need to be restored. Follow the steps outlined below … [Read more...] about rpm: error while loading shared libraries: invalid ELF header