The Problem If a command is used with sudo (for e.g. sudo yum clean all) it takes time to execute. [21:29]$ sudo yum clean all [sudo] password for test@geeklab: Loaded plugins: package_upload, product-id, search-disabled-repos, subscription-manager Cleaning repos: production-rhel-x86_64-workstation-7.4 rhel-7-server-rpms Cleaning up everything Maybe you want: rm -rf /var/cache/yum, to also free up space taken by orphaned data from disabled or removed repos [21:33]$ In the above … [Read more...] about Commands used with sudo takes time to execute
Oracle RAC instabilities due to firewall (netfilter/iptables) enabled on the cluster interconnect
Oracle Clusterware may not startup (root.sh on second node fails with "Failure at final check of Oracle CRS stack."), due to a firewall (such as iptables on Linux) configured on the cluster interconnect. Other symptoms include moderate to serious performance and stability issues, directly related to such firewalls. Examples are false evictions of nodes, 'IPC SEND/RECEIVE TIMEOUT' and slow/uneven performance. Oracle RAC uses the cluster interconnect to send buffer cache blocks between … [Read more...] about Oracle RAC instabilities due to firewall (netfilter/iptables) enabled on the cluster interconnect
How to permanently modify the kernel command line in CentOS/RHEL 8?
RHEL 8's boot loader, Grand Unified Boot Loader (GRUB2) differs from the GRUB2 in RHEL 7. An update to Red Hat Enterprise Linux 8 Beta results in /etc/default/grub changes no longer being included when issuing "grub2-mkconfig -o /boot/grub2/grub.cfg". It seems that at least some options set there are now silently ignored. There are multiple different paths to achieve alterations to the kernel boot parameter option. grub2-editenv The grub2-editenv utility is actually the recommended path … [Read more...] about How to permanently modify the kernel command line in CentOS/RHEL 8?
Modifying /etc/default/grub – RHEL 7 V/s RHEL 8
RHEL 8's boot loader, Grand Unified Boot Loader (GRUB2) differs from the GRUB2 in RHEL 7. An update to Red Hat Enterprise Linux 8 Beta results in /etc/default/grub changes no longer being included when issuing "grub2-mkconfig -o /boot/grub2/grub.cfg". It seems that at least some options set there are now silently ignored. GRUB2, with RHEL 8, builds the various kernel boot entries using a new specification called BLS. The /etc/grub2.cfg file no longer has various menuentry entries, but instead … [Read more...] about Modifying /etc/default/grub – RHEL 7 V/s RHEL 8
What is the MySQL Enterprise Monitor?
The post provides an overview of what features the MySQL Enterprise Monitor provides and how it can be used to improve MySQL administration and performance. Provided as part of MySQL Enterprise, the MySQL Enterprise Monitor is a Virtual DBA assistant that helps MySQL DBAs manage more MySQL servers, tune MySQL servers, and find and fix problems with MySQL database applications before they can become serious problems or costly outages. Running completely within the corporate firewall, the … [Read more...] about What is the MySQL Enterprise Monitor?
Howto Verify If a Bootblk is Installed on the Boot Disk (SPARC)
This can be useful in troubleshooting if the system fails to boot with a suspected bootblk issues, or if you suspect something in the OS keeps overwriting the bootblk. For Solaris 10 Below is the output from a Solaris 10u4 with UFS, Solaris 10u6 with UFS, and a Solaris 10u6 with ZFS bootblock. The bootblk version changed from s10u6 onwards. This is why the output differs between s10u6 and earlier versions. S10U1 through U5 UFS root: # dd if=/dev/rdsk/c0t0d0s0 bs=1b count=1 iseek=1 | od … [Read more...] about Howto Verify If a Bootblk is Installed on the Boot Disk (SPARC)
How to use strace to trace system calls made by a command in Linux
Introduction The command strace is used to trace system calls and signals. It is a great tool to use when debugging an application and is often requested by the support engineers to examine certain issues which may arise within the operating system and its programs. Usage To record the system calls issued by running command and output trace information to a file called /tmp/strace.txt, run the following: RHEL 6.7+ and RHEL 7 with strace 4.7 or above: # strace -fvttTyyx -s 4096 -o … [Read more...] about How to use strace to trace system calls made by a command in Linux
Starting iptables Fails with Error “Another app is currently holding the xtables lock”
The Problem Updating the package iptables to iptables-1.4.7-16.0.3.el6, the service fails to start after a stop. # service iptables stop iptables: Setting chains to policy ACCEPT: filter [ OK ] iptables: Flushing firewall rules: [ OK ] iptables: Unloading modules: [ OK ] # service iptables start iptables: Applying firewall rules: Another app is currently holding the xtables lock. Perhaps you want to use the -w option? [FAILED] The Solution Iptables is being lock, and is creating … [Read more...] about Starting iptables Fails with Error “Another app is currently holding the xtables lock”
How to limit bandwidth or traffic for applications using iptables
The Ask The user wants to limit apache's bandwidth of incoming and outgoing traffic for each client IP addresses using iptables in the CentOS/RHEL box. How can we implement this? The Answer You can limit the bandwidth with "hashlimit" module of iptables. From the man page of "iptables" command: # man iptables ... hashlimit hashlimit uses hash buckets to express a rate-limiting match (like the limit match) for a group of connections using a single iptables rule. … [Read more...] about How to limit bandwidth or traffic for applications using iptables
How to Manually Bring up the Network or specific interface in CentOS/RHEL (without using NetworkManager or the network service)
How do I gain network access to a system for troubleshooting? The network service and/or NetworkManager service are not working. How can I bring networking up to troubleshoot further? How can I bring up an interface for the current boot only? Note: These settings are not persistent and will only work for the current boot. Leaving NetworkManager running, running ifup or ifdown, or starting/stopping/restarting the network service has the potential to change these manually-entered … [Read more...] about How to Manually Bring up the Network or specific interface in CentOS/RHEL (without using NetworkManager or the network service)