Sometimes you need an older version of Hadoop — for compatibility with existing jobs, to reproduce bugs, or to match a specific cluster environment. The Apache Hadoop project maintains an archive of all past releases. From the Apache Archive All Hadoop releases are available from the Apache Software Foundation’s distribution archive: https://archive.apache.org/dist/hadoop/common/ Browse the directory…
After a libvirt upgrade, VMs fail to start with the error: error: Failed to start domain kvm1 error: Network not found: no network with matching name ‘default’ This happens when the default NAT network (virbr0) isn’t automatically created during the upgrade. Quick fix: Restore the default network The fastest solution is to recreate the default…
Getting kernel function call stacks is essential for debugging driver issues, understanding kernel behavior, and performance profiling. The approach depends on what you’re trying to trace: live kernel execution, crash analysis, or post-mortem inspection. Using ftrace The kernel’s built-in ftrace framework is the first tool to reach for. It’s zero-overhead when disabled and has minimal…
When trying to mount an encrypted EncFS directory as a normal user, you may encounter this error: $ encfs -s ~/t/.enc ~/t/enc EncFS Password: fuse: failed to exec fusermount: Permission denied fuse failed. Common problems: – fuse kernel module not installed (modprobe fuse) – invalid options — see usage message Even though the same command…
When running Ubuntu on older servers like Dell PowerEdge systems with legacy graphics cards (Matrox G200eR2, etc.), you may encounter extremely slow desktop performance. The issue typically stems from the X server falling back to unoptimized drivers or incorrect video mode detection. Identifying the problem First, check your current graphics configuration: lspci | grep -i…
The bottom panel in GNOME Classic displays the window list via the “Window List” extension. If you don’t use it, there are several ways to remove it depending on your approach. Method 1: Context menu removal (Recommended) The simplest approach if your GNOME version supports it: Hover over a blank area of the bottom panel…
[md] The RTL8192cu is a legacy USB WiFi adapter that’s still in use, but it has known stability issues on modern kernels. If your adapter keeps dropping connections or fails to resume after sleep, you’re likely hitting the same power management bug that affects many devices. ## Disable Power Management The most reliable workaround is…
PARSEC is a widely-used CPU-bound benchmark suite containing real applications and complex third-party library dependencies. The installation can be challenging due to these external requirements, but following this guide will get you up and running. Prerequisites Before starting, install the required build tools and libraries: sudo apt-get update sudo apt-get install build-essential pkg-config gettext autoconf…
Error handling is fundamental to Go development. Often you’ll need to convert an error to a string for logging, displaying to users, or including in API responses. Go provides several straightforward approaches. Using the Error() Method Every error in Go implements the error interface, which has a single method: Error() string. The simplest conversion is…
When you’re working in a Makefile, you often need to reference files relative to where the Makefile itself is located. This is especially useful for multi-directory projects or when your build system needs to know its own location. The Solution Make provides the MAKEFILE_LIST variable, which contains the names of all makefiles that have been…
The usermod command is the standard tool for modifying user accounts. To change a username, use the -l (or –login) option: sudo usermod -l user1 u1 This changes the login name from u1 to user1. However, there’s an important caveat: usermod only updates the /etc/passwd file. The user’s home directory, mail spool, and other resources…
The standard systemctl enable command should work for rpcbind.service, but if you’re seeing it fail to start after reboot, there are several approaches to troubleshoot and fix the issue. Check the Current State First, verify the actual status: systemctl status rpcbind.service systemctl is-enabled rpcbind.service If is-enabled returns disabled, the service wasn’t properly enabled. Check for…
If you’ve set up passwordless SSH login with key-based authentication but lftp keeps prompting for a password, you need to explicitly configure it to use your SSH keys. The basic approach The simplest method is to pass an empty password to lftp, which signals it to fall back on SSH key authentication: lftp -u user,…
When you source a script using . script.sh or source script.sh, the $0 variable doesn’t point to the sourced script—it stays as the path of the parent shell or calling script. This creates a problem if you need the sourced script to know its own location. The solution: use ${BASH_SOURCE[0]} The ${BASH_SOURCE[0]} variable holds the…
When writing system administration scripts, you often need to check if a user account exists before taking action. There are several reliable methods to accomplish this. Using id command The id command retrieves user information and returns a non-zero exit code if the user doesn’t exist. This makes it ideal for conditional testing: user=”hello” if…
If you need to jump to a particular byte position in a file, Vim provides the goto command. This is useful when debugging binary files, working with hex editors, or when error messages reference byte offsets. Using the goto command In normal mode, press go followed by the byte number: 20go This moves the cursor…
Getting the full or abbreviated commit hash is essential for scripting, CI/CD pipelines, and version tracking. Here are the standard approaches. Full commit SHA-1 To retrieve the complete commit hash of the current HEAD: git rev-parse HEAD This outputs the full 40-character SHA-1 hash. It works in any Git repository state and is reliable for…
[md] The dd command doesn’t evaluate arithmetic expressions in its parameters. If you try this: $ dd if=/dev/zero of=./4Ktest100M bs=4KB count=25000*9 dd: invalid number ‘25000*9′ You’ll get an error because dd expects literal numeric values, not expressions. The shell doesn’t expand 25000*9 as arithmetic — it’s passed to dd as a literal string. ## Using…
When you need to access files from a Xen guest’s disk image without booting the VM, you can attach and mount its partitions directly on the host using kpartx. This is useful for recovery, forensics, backup verification, or migrating data between systems. Using kpartx to expose partitions The kpartx utility creates device mappings for partitions…
Getting the directory path of a running script is a common requirement in bash, whether you’re sourcing files, building paths to config directories, or navigating relative to the script itself. The naive approach often fails with symbolic links or when the script is sourced rather than executed directly. The Problem Using $0 alone is unreliable….