How to change boot into text console or GUI in Raspberry Pi
There are two ways to configure Raspberry Pi OS to boot into console or GUI mode. First, run # raspi-config, select "System Options", then "Boot / Auto Login".
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81 articles on this topic
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.
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.
How to send Email with netcat
There are many ways to send mail from the Linux command line. For repeated system tests, netcat can send a prepared message with one command.
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 change an iDRAC password using Racadm
Reset an iDRAC password directly from the server through OpenManage using racadm. Install OpenManage before following these steps.
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.
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
Monitor multiple logs in a single shell with MultiTail
tail is widely used for viewing logs in real time (tail -f /var/log/logfile). MultiTail provides similar functionality with multiple windows in one console.
Bash Autocomplete feature on CentOS Linux
Bash autocompletion makes Linux work much more convenient. For me it is essential because it makes commands quicker to use.
Definition of DNS status: NXDOMAIN, NOERROR and SERVFAIL
NXDOMAIN, NOERROR, and SERVFAIL are DNS query statuses. Understanding them helps interpret what happened when looking up domain records.
How to improve DNS lookups on Linux system
Listing multiple DNS servers in /etc/resolve.conf defines primary and secondary DNS servers. If the primary fails, the system switches to the secondary after a timeout.
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.
NUMA Architecture and MySQL
NUMA is a new architecture for multiprocessor systems. Each physical processor has its own memory, allowing faster memory access than the older architecture. Linux…
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 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 set a crontab to run command on the last day of every month.
Linux crontab alone cannot specify the last day of a month or its first Saturday. These scripts add that control to scheduled commands.
How to broadcast a message to all users and direct message to some user
Administrators have several ways to send messages to users logged in to a text-mode system. This article covers broadcasting to all users and sending directly to one user.
Linux last Command – List Users Who Logged In
When you need to check login details, what comes to mind first? Many would look in /var/log/secure because it stores login history, but that can be cumbersome…
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.
Add Windows (TrueType) Fonts in GNOME desktop
This expands on step 2 of Add Thai fonts in Linux, explaining how to open Nautilus and browse to fonts:// to add Windows TrueType fonts to GNOME.
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 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.
Change I/O Disk Scheduler without Reboot
There are four I/O schedulers for hard disks and block devices: anticipatory, noop, deadline, and CFQ. CFQ is usually the default. To change the I/O scheduler…
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 Set up GRUB to boot from both disks of mirrored RAID
On Linux software RAID 1, GRUB normally boots from the primary disk. Configure it on the secondary disk too so the system can boot if the primary fails.
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…
Rescan SCSI to add, remove SCSI device without rebooting
To rescan an entire SCSI bus and re-register all devices found: rescan SCSI so the system sees a new device. On some Linux systems, this also adds or removes devices.
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…
Autofs version 5 Features
The new autofs version (autofs5) adds features that improve interoperability with other systems. The new features include: Direct map support, which provides a mechanism to automatica…
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.
Set up your Linux for Wake On LAN (WOL)
Wake on LAN starts a server through a network command from another machine. Configure both the server receiving the wake command and the client sending it.
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…
Add Thai Fonts to Linux
Some Linux versions display Thai vowels in the wrong positions because they lack fonts that render Thai correctly. There are several ways to fix this…
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.
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.
Export a directory with NFS v4
A major difference between NFS v4 and earlier versions is the ability to export a single directory in a way similar to an FTP or web server, such as exporting /shared.
Lock user after a set number of login attempts but also automatically unlock after 5 minutes
This article explains how to lock a user after a set number of login attempts using the pam_tally module in PAM.
Force users to change their passwords upon the first login
Linux can force users to change their passwords at their next login by locking the account, expiring the password, and unlocking the account.
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
How to enable xdmcp
The XDMCP configuration file has moved from /etc/X11/gdm/gdm.conf to /etc/gdm/custom.conf. To enable XDMCP, edit the section under xdmcp.
Reduce a non-root LVM.
This example reduces a 10 GB LVM volume to 8 GB, assuming it is mounted at /data, by shrinking the filesystem before reducing the logical volume.
View the commented lines of text in a config file
Use grep to display configuration lines that begin with particular characters. This helps inspect comments and review configuration settings.
Configure the shell to logout automatically after a period of idle time.
On systems with many users, users who leave without logging out waste system resources. This method addresses that and also improves security…
Access a USB flash drive in Linux.
Linux normally mounts USB flash drives or thumb drives automatically when you plug them in. Sometimes it does not, which can frustrate new users…
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.
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.
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…
Extract files from an RPM package
RPM (Red Hat Package Management) packages are installation files for Red Hat Linux distributions. They are popular because software is easy to install and remove.
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.
Map Of The Linux File System
Here is a diagram of Linux directories for Ubuntu beginners and users who are unsure where things are stored. Many thanks to Scott Gilbertson of Wired.
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…
Force fsck on the next boot sequence
To have Linux check every partition's file system after a reboot, use these commands as root. Create /forcefsck in the root directory to force a check on the next boot…
Change the behavior of the copy (cp) command overwrite the existing file without prompt
Edit $HOME/.bashrc, because Red Hat adds alias cp='cp -i'. Thus the -r option has no effect. Comment out alias cp='cp -i' with #, then log out and log back in…
When you forgot root password.
What can you do when you cannot log in because your password is rejected? After reading this article, you will be able to resolve the situation easily. I will cover two bootloaders…
Make dd give a progress report.
Many of you have probably used dd, but it does not show how far it has progressed. This article explains how to view dd's progress.