How to stress test the memory on linux
stress tests CPU, memory, I/O, and HDD workloads on POSIX systems. This article shares commands to use 95% of memory to check for memory problems.
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How to fix memory leak from big nfs_inode_cache
A Linux server was reported to be using over 90% of its memory, but its administrator could not identify a memory-heavy process. My initial check with free showed nothing unusual.
SysVinit and systemd command comparison table
RHEL 7 changes its service manager from SysVinit to systemd, offering parallel operation, mount point handling, and cgroups support. These tables compare their commands.
How to fix yum return Segmentation fault error
On CentOS 5, yum may return a Segmentation fault error, for example: [root@ezylinux ~]# yum update bash. base | 1.1 kB 00:00…
How to fix chroot return "Exec format error"
A chroot Exec format error in Red Hat/CentOS rescue mode usually means the running environment and target commands use different architectures.
How to install CentOS 6 for Zimbra Mail Server
Zimbra supports only a few Linux distributions. One of the supported distributions is the very popular CentOS 6. This article explains how to install CentOS 6.
Setting a schedule delayed shutdown
Linux can be shut down in several ways, usually immediately. Scheduling a shutdown and notifying other remote users gives them time to prepare.
How to fix yum error: database disk image is malformed
If yum reports "Error: database disk image is malformed" while installing or updating packages, as shown below: [[email protected] ~]# yum install ruby Loaded plugin
Find out which processes are using swap space
A script to identify processes using SWAP on a server. It displays process details and the amount of swap space each process uses. #!/bin/bash # Get current swap usage for all
Steps to install Ruby Version Manager (RVM) on CentOS 6
CentOS 6 ships with Ruby 1.8.7. Ruby Version Manager (RVM) lets applications use other Ruby versions without changing the main system.
How to install whois using yum on CentOS
whois queries domain information directly, helping administrators check domain ownership, expiry dates, or use the information in scripts.
How to check Zimbra version
There are several ways to check the Zimbra version: through a web browser, commands, or the installation history file. I have collected these methods for checking the Zimbra version…
How to get physical number of CPU sockets on Linux server
On a Linux server, you can check how many physical CPU sockets it has without opening the machine. The command is dmidecode. Installing dmidecode…
How to check status, start and stop on Zimbra service
Use zmcontrol to check the operating status of Zimbra. It can also start and stop Zimbra. To use it, you must first log in as the zimbra user…
How to update dell server firmware with Dell Unified Server Configurator
Dell Unified Server Configurator can automatically update Dell server BIOS, network cards, iDRAC, RAID controllers, and other firmware when the server has internet access.
How to list the files from rpm package by rpm or yum-utils
You can list the files in an RPM package, whether installed or not, in two ways: rpm and repoquery. Here is how to use both commands…
How to build RPM package for the Coova-chilli with CentOS 5
Coova chilli is hotspot software that I believe branched from Chilli hotspot, which appears to have stopped development. RPM files for RedHat Enterprise or CentOS can be hard to find.
How to install Linux USB drives using UNetBootin tool
UNetbootin creates a Linux Live USB on a flash drive from a downloaded ISO file or one it downloads from the Internet. It supports distributions including Ubuntu.
How to install Dell OpenManage Server Administrator (OMSA)
Dell OpenManage Server Administrator (OMSA) monitors hardware and alerts, helps troubleshoot hardware, configures RAID, and integrates with monitoring software.
How to rebuild corrupted RPM database
Today I repeatedly used yum to install, update, and erase packages. It then hung for a long time during an uninstall. Wondering why it was taking so long, I checked its process…
RPM repository of RPM add-on packages for Red Hat Enterprise Linux and CentOS
A collection of RPM repositories useful when you need packages unavailable on the installation media or in the base repository for Red Hat Enterprise Linux and CentOS. RPMforge installation commands: RHEL6 / CentOS-6, i386…
How to change Host ID for Linux
The hostid command displays a Linux machine's ID. Linux generates a host ID at installation, and reinstalling generates a different one, which can affect software licenses tied to it.
Download package using yum command
Yum installs packages online on Red Hat Linux distributions, much like apt-get on Debian or Ubuntu, and handles package dependencies.
Different types of kernel packages in Red Hat Enterprise Linux
Red Hat provides several kernel packages with different capabilities. Installing an unsuitable kernel can prevent the system from recognizing all installed hardware.
Convert RPM to DEB or DEB to RPM
Sometimes you need a package but only a package for another distribution is available. What can you do? This article explains converting RPM to DEB and DEB to RPM…
Red Hat 4, 5 take a very long time to boot and iostat output incorrect
Slow boots of more than two hours or incorrect iostat output, such as 200% CPU utilization, can occur on x86 or x86_64 because of mismatched timers.
Find Out Which RPM Installed a Specific File by rpm or yum Command
Use rpm or yum to find which package installed a file or command. yum requires repository access unless the required data is already cached.
How to check the SUSE Linux Enterprise and Open Enterprise Server for Linux version
Use `uname -r` to check the kernel version and compare it with the SUSE Linux Enterprise and Open Enterprise Server for Linux versions.
How to read memory usage with the free command
Linux uses RAM extensively to cache local and remote filesystem and disk data. The free command shows used, free, cached, and application memory.
How to check the version of Red Hat Enterprise Linux and CentOS Linux
Check Red Hat Enterprise Linux or CentOS versions by reading /etc/redhat-release or using uname to identify the release from its kernel version.
Yum, Yellow dog Update, Modified and How to use Yum
Yum, or Yellow dog Update, Modified, manages RPM package installation, removal, and updates, resolving dependencies from configured repositories.
Why CPU stats between ps and top Command are Different
The difference between CPU statistics from ps and top is that ps calculates CPU utilization as total CPU time divided by the task's running time, while top displays a percentage of overall CPU time…
How to Configure yum Show Availble updates from exclude list
yum normally hides packages listed under exclude in yum.conf, so yum update does not show which newer versions are available for those packages.
Enable Core Dumps for Daemons or Services in Red Hat Enterprise Linux
Daemons normally run as background processes and can be started with service commands or init scripts. Core dumps help debug programs and investigate errors.
Enable Dynamic CPU Speed Scaling in Linux
Linux's cpuspeed power-saving technology has developed since Intel and AMD began adding DVS (dynamic voltage scaling) to CPUs, adjusting CPU voltage to reduce power use.
Controlling Core Dump Files in Linux
Core dumps are created when programs crash or access unauthorized memory, helping programmers debug problems. Linux provides settings to control their size, names, and location.
How large is the virtual address space for a process
In Linux, choosing a CPU and kernel suited to the application's requirements helps the system run stably. x86_64 (AMD64, EM64T) processors are 64-bit processors…
How to know x86 system capable running 64-bit software
How can you tell whether your system supports 64-bit, 32-bit, or 16-bit applications? This article explains Long mode and Legacy mode.
Free memory by flushing pagecache and slabcache
You can free memory on demand with a simple command that clears the Linux pagecache and slabcache. Write 1 to free pagecache, 2 to free…
How to increase the I/O priority of processes
In Linux, you can increase or decrease I/O access priority per process with ionice, which displays and changes the I/O scheduling class and priority of a process…
Increase the Virtual Console Resolution
The virtual console normally displays 80x24 lines. For a higher resolution, edit /boot/grub/grub.conf and add a vga setting to the kernel line.
Find information on the maximum amount of memory that system can handle
On newer Linux systems, dmidecode reports the maximum memory capacity supported by the system BIOS.
Find which RPM contains a specific file
On Red Hat systems, use rpm, yum, or up2date to find which RPM package contains a particular file.
Regenerate a GRUB device.map file
device.map maps hard disk devices to GRUB device names and is created during operating system installation. Recreate it if it is missing.
How many of swap space for Linux system
Many people wonder how much swap to create during installation. The usual rule is at least twice the RAM, but if the system has a lot of RAM, is twice as much really necessary…
Rebuild the kernel (complie kernel) from Kernel source.
Compiling a Linux kernel may sound difficult, but it takes only a few steps after preparing the compiler, libraries, and other development tools.
Determine x86-compatible Intel system is multi-processor, multi-core or supports hyperthreading
Many people know Hyperthreading (HT), also called Symmetric Multi-Threading (SMT), a feature of Intel x86 CPUs found in older Pentium 4 and some Xeon processors…
After installation machine hangs during first boot
A Red Hat Enterprise Linux installation may hang on first boot because of an Advanced Power Management (APM) issue. Try disabling APM with apm=off.
How to use command to restart or shut down Linux system
Commands to shut down Linux: #shutdown -h now #init 0 #halt #poweroff. Commands to reboot: #reboot #init 6 #shutdown -r now.
Diskdump report error messages when restart the diskdump service
After changing the diskdump configuration and restarting its service, errors may appear in /var/log/messages: diskdump: diskdumpctl: failed to add /dev/hdb! diskdump: a
What is a Red Hat Enterprise Linux Installation Number and where do I get it?
Resolution: The Red Hat Enterprise Linux 5 Installation Number is a 16-character hexadecimal text string used during the installation process. The installation number enables a user to install the ful
Disable some CPUs within Red Hat Enterprise Linux 5 without rebooting the system
Warning: check that your hardware supports CPU hot swapping before trying these commands; otherwise the hardware may be damaged.
Copy a list of print queues from one server to another
On Red Hat Linux clones, print queue settings can be exported and copied to another print server for use or load sharing.
RedHat 5 and RedHat 5.1 hang at the final stage of reboot or shutdown
RedHat 5 and RedHat 5.1 may hang at the final stage of reboot or shutdown because of a cpufreq bug that causes a deadlock when its module is unloaded.
[Bug]Red Hat Enterprise Linux 4.5 system panic when I boot into the largesmp kernel
On RedHat V4.5, the largesmp kernel panics during boot on systems with more than eight CPUs and NUMA disabled. RedHat says the bug will be fixed in the next update.
What are the memory and CPU limits of the largesmp kernel in Red Hat Enterprise Linux 4?
Red Hat Enterprise Linux 4 update 3 and later provides a largesmp kernel for systems with many CPUs, available for x86_64, ia64, and ppc64.
Install RedHat Enterprise Linux 5, Centos 5
Linux can be installed in several ways, including CD-ROM, hard disk, network, and Red Hat Network. This article focuses on installation from CD-ROM.
How do I turn off the bell/beep
In Linux, you can disable the beep if you do not want it. The sound comes from the pcspkr module. Use: # rmmod pcspkr. To disable it every time the machine starts…
Find the number of sockets a process currently has open
To find how many sockets a process has open on Linux, first identify its PID using $ ps -aef | grep, then count its sockets.
Check boot parameters were passed to the kernel
To see the kernel's boot parameters, use # cat /proc/cmdline. ro root=LABEL=/ rhgb quiet
How to Remove LILO, GRUB or Master Boot Record from system
A hard disk generally stores the system bootloader's binary code in the first 512 sectors, or 512 bytes. LILO or GRUB embeds itself in the master boot record…
Change my hostname or the machine name in Red Hat Linux.
There are several ways to change a Red Hat or Red Hat clone hostname, including hostname without restarting the network service.