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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I need to audit what root users typed in their sessions. Try: sudo tail -f /root/.bash_history /home/*/.bash_history 2>/dev/null Info: Streams multiple history files concurrently with header markers for simple multi-user monitoring. Examples: $ echo 'export HISTTIMEFORMAT="%F %T "' >> ~/.bashrc # Add precise timestamps to history $ echo 'PROMPT_COMMAND="history -a"' […]
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I deleted sensitive files but worry forensics could recover them. How do I wipe free space? Try: sudo dd if=/dev/zero of=/wipe-file bs=1M status=progress; sudo rm /wipe-file Info: dd fills remaining disk free space with zeros, overwriting blocks of previously deleted files before rm releases the space. "No space left" is […]
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Something is pegging my CPU. How do I pinpoint it with real-time refresh? Try: top -b -n 1 -o %CPU | head -20 Info: Running top in batch mode (-b -n 1) executes a single non-interactive snapshot, while -o %CPU dynamically sorts processes by CPU utilization for quick diagnostics and […]
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DNS is failing intermittently. How do I trace the resolution path? Try: dig +trace +noanswer google.com Info: dig +trace performs iterative DNS lookups from root servers (.), down to TLDs (.com), and final authoritative servers to isolate propagation and delegation bottlenecks. Examples: $ dig @8.8.8.8 example.com # Query specific upstream […]
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A single TCP connection seems slow. Can I measure its real throughput? Try: sudo iftop -i eth0 -nNP -f 'port 443' Info: iftop acts as top for network bandwidth, tracking individual connections and displaying 2s/10s/40s moving averages to pinpoint bandwidth hogs. Examples: $ sudo iftop -i eth0 # Launch interactive […]
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I keep typing shutdown on the wrong server. How do I protect against this? Try: sudo tee /etc/molly-guard/run.d/50-prod-check <<'EOF' > /dev/null #!/bin/bash if [[ -f /etc/is_production ]]; then read -r -p "PRODUCTION server! Type the hostname to confirm shutdown: " input [[ "$input" == "$(hostname)" ]] || exit 1 fi […]
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