Master Linux administration, command-line tools, system configuration, and single-machine systems. Explore our full academy at: https://www.systutorials.com/linux-systems-admin-academy/
The tilde expansion ~username works fine when the username is literal, but fails when the username is stored in a variable like ~$user. Bash doesn’t perform tilde expansion on variables by default—it only expands ~ at the beginning of a word before variable expansion happens. Using eval The most common approach is to use eval:…
When you try to unmount a filesystem, Linux sometimes refuses with a “device is busy” error. This safety mechanism prevents data loss when processes are actively using the filesystem. But there are legitimate cases where you need to force an unmount: a dead NFS server, a failed USB device, or a hung mount that won’t…
When Linux fails to boot with the error message “sulogin: can not open password database” despite /etc/passwd and /etc/shadow appearing intact, SELinux is often the culprit. The files exist and have correct content, but SELinux context labels are missing or corrupted, preventing the login process from reading them. Diagnose the Problem Boot into the initramfs…
Sorting text file lines by their length is useful for analyzing text patterns, finding anomalies, or preparing data for processing. Here are the most practical approaches. Using awk with sort The standard approach combines awk to calculate line length with sort to order them: awk ‘{ print length(), $0 | “sort -n” }’ /path/to/text/file This…
When you run journalctl without options on a system with years of log history, it can take seconds or even minutes to parse everything. The slowness comes from journalctl loading and deserializing potentially gigabytes of journal data. The solution is targeted querying — you almost never need the entire journal, so restrict what journalctl reads…
For exhibition displays, kiosks, or continuous playback scenarios, you need a video player that can go fullscreen and loop indefinitely without user intervention. Using mpv (modern replacement) MPlayer is largely unmaintained. mpv is the actively developed fork and recommended alternative: mpv –fullscreen –loop=inf video.mp4 Or use the shorthand flags: mpv -fs –loop=inf video.mp4 The –loop=inf…
Bash provides several straightforward ways to test whether a string contains a substring. The best approach depends on your use case and performance requirements. Using [[ ]] with glob patterns The fastest and most Bash-native method is the [[ conditional construct with glob patterns: if [[ “$string” == *”substring”* ]]; then echo “Found it!” fi…
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 shell arithmetic expansion The…
When accepting path input in Bash scripts, users might provide /path/to/dir/ or /path/to/dir. Normalizing these to a consistent format without the trailing slash is a common requirement. The Problem You need a reliable method that: Removes trailing slashes if present Works with both files and directories Handles paths that already lack a trailing slash Works…
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….
LevelDB allows key ranges to overlap across SSTables in Level 0, unlike higher levels where overlaps are eliminated through compaction. This design choice is fundamental to LevelDB’s write performance and is worth understanding in detail. Why Level 0 Allows Overlaps The reason comes down to write efficiency. When you write data to LevelDB, it follows…
By default, xargs appends its input as arguments at the end of the command. This works fine when you need a utility once per item, but becomes problematic when you need to reference the same input multiple times in different positions. The Problem Consider renaming files by appending .bak to each filename. You might try:…
When you run a command like this in Bash: ssh host1 hostname &; ssh host2 hostname & You get an error: bash: syntax error near unexpected token `;’ The issue stems from how Bash interprets command separators. The & and ; characters are both command terminators, but they serve different purposes, and Bash has strict…
Firefox ships with several search engines pre-configured, but the default varies by region and Mozilla’s partnerships. If you want Google as your primary search engine on Linux Mint, the process is straightforward. Access Firefox Search Settings Open Firefox and navigate to about:preferences#search in the address bar, or go through the menu: ☰ (hamburger menu) →…
If you’ve downloaded a Windows ISO file but lack a DVD drive, creating a bootable USB installation drive is straightforward. This works for Windows 10, 11, and later versions. Using the Windows Media Creation Tool Microsoft’s official approach is the Windows Media Creation Tool, which is more current and reliable than older third-party utilities. Download…
When stop-dfs.sh fails to cleanly terminate DataNode processes, you’re left with orphaned Java processes consuming resources and potentially causing cluster issues. This happens most often after ungraceful cluster shutdowns or when the standard stop script encounters communication problems with specific nodes. Understanding the Problem The typical symptom is stop-dfs.sh reporting that certain nodes have no…
Extracting images embedded in PDF files is straightforward on Linux with several reliable tools. Here are the most practical approaches, from GUI tools to command-line solutions. GUI Tools LibreOffice Draw remains the simplest option if you prefer a graphical interface. Open the PDF file in LibreOffice Draw, right-click on any image, and select “Save Image…
If your iPhone contacts search is returning “No results” after an iOS update, the issue is often a corrupted contacts database or a syncing problem with your contacts source. Here are the most effective fixes. Check Your Contacts Source First, verify where your contacts are actually stored. Go to Settings > Contacts > Default Account…
Firefox on iOS has improved significantly since the early days, but understanding what syncs and what doesn’t remains important for managing bookmarks across devices. Current sync capabilities As of 2026, Firefox sync does support bookmarks across iOS and desktop, but with important limitations. When you enable Firefox sync on your iOS device and link it…