Which exact binary does a systemd service execute? Try: systemctl show nginx -p ExecStart --no-pager Info: The systemctl show command displays unit properties, extracting exact binaries, arguments, and configuration file paths via specific property filters. Examples: $ systemctl show nginx --all # Dump all available properties for the service unit […]
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A rogue script is calling an external API. How do I find and stop it? Try: sudo ss -tnp dst 203.0.113.45 Info: Filters socket connections by destination IP to expose associated processes and PIDs for immediate termination. Examples: $ sudo ss -tnp 'dst 192.168.1.0/24' # Filter connections targeting an entire […]
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My config reload reads a half-written file. How do I update it safely? Try: mv /etc/myapp/config.new /etc/myapp/config.json Info: Same-filesystem file renames are atomic at the inode level, ensuring readers see either the complete old file or the new file. Examples: $ sed -i.bak 's/old/new/' file # Perform an in-place file […]
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I rsync'd two folders. How do I verify they truly match? Try: diff -rq /source /destination Info: Recursively compares directories and reports differing files or unique items without printing full diff contents. Examples: $ diff -rq /a /b | grep -v '^Only' # Compare file contents only, ignoring missing files […]
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How do I see what environment vars a running daemon was started with? Try: sudo cat /proc/3456/environ | tr '\0' '\n' Info: Reads null-separated initial environment variables from the process proc entry and translates them into readable lines. Examples: $ sudo strings /proc/3456/environ # Alternative method using strings to extract […]
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How do I auto-rebuild my project when source files change? Try: while inotifywait -r -e modify,create,delete ./src/; do make build; done Info: inotifywait exits after a single file event, allowing a simple while loop to trigger builds on modification without external watchers. Examples: $ while inotifywait -e modify ./style.css; do […]
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A buggy script is eating all my RAM. How do I cap its memory usage? Try: ulimit -v 524288 Info: Restricts virtual memory for the current shell session and its child processes. Examples: $ ulimit -a # Display all current resource limits for the session $ ulimit -t 60 # […]
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How do I check SSL certificate expiry dates on all my servers in bulk? Try: for host in server1.example.com server2.example.com api.example.com; do echo -n "$host: "; echo | openssl s_client -connect $host:443 -servername $host 2>/dev/null | openssl x509 -noout -enddate; done Info: echo | openssl s_client makes a quick TLS […]
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My script is slow but I don't know if it's CPU, I/O, or waiting. How do I find out? Try: /usr/bin/time -v ./slow_script.sh 2>&1 | grep -E 'Elapsed|CPU|Maximum|context|wait' Info: Profiles resource bottlenecks by outputting detailed timing, CPU utilization, page faults, and context switches. Examples: $ /usr/bin/time -v command 2>&1 | […]
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I need to run an untrusted binary without exposing my whole system. How? Try: sudo mkdir -p /jail/{bin,lib,lib64} Info: chroot restricts a process to a specified root directory, preventing it from accessing the rest of the filesystem. Examples: $ ldd /bin/bash # List all required shared libraries for a binary […]
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I have duplicate-looking files. Are they hardlinks or real copies? Try: find /home/linuxteck -type f -links +1 -printf '%i %n %p\n' | sort Info: Finds files sharing inodes and link counts to identify hardlinks. Examples: $ find /path -samefile /path/to/original # Locate all hardlinks referencing a specific file $ ls […]
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My encrypted data disk needs password every boot. How do I automate it safely? Try: sudo cryptsetup luksAddKey /dev/sdb1 /root/keyfile.bin Info: Adds a keyfile slot to LUKS for automated boot decryption. Examples: $ sudo cryptsetup luksDump /dev/sdb1 # Inspect active LUKS key slots $ sudo cryptsetup luksRemoveKey /dev/sdb1 # Revoke […]
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How do I record my terminal session and replay it like a video? Try: script --timing=session.timing session.log Info: Records terminal input/output alongside precise timing data for real-time playback. Examples: $ script -t 2>session.timing session.log # Legacy syntax for timing file capture $ scriptreplay --timing=session.timing session.log -d 2 # Replay session […]
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My logs are eating 50GB. How do I compress all old ones in one pass? Try: sudo find /var/log -type f \( -name '*.log' -o -name '*.log.?' \) -mtime +7 ! -name '*.gz' -exec gzip -9 {} + Info: Recursively finds and compresses log files older than 7 days using […]
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I need to generate secure passwords without using a website. Try: openssl rand -base64 32 | tr -d '/+=' | cut -c1-20 Info: Generates cryptographically secure random bytes from OpenSSL. Examples: $ pwgen -s 20 # Generate fully random 20-character passwords $ head /dev/urandom | tr -dc A-Za-z0-9 | head […]
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My build is slow because of disk I/O. How do I use RAM as a filesystem? Try: sudo mount -t tmpfs -o size=4G,mode=1777 tmpfs /mnt/ramdisk Info: tmpfs creates an ultra-fast temporary RAM filesystem (~7x faster than SSD), ideal for build caches, temp files, and test databases. Data vanishes on reboot. […]
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