Linux and DevOps Cheat Sheets - Page 3

On RHEL 7, CentOS 7, and other legacy RPM systems, yum installs and removes packages from configured repositories. It resolves dependencies, supports package groups, and records transaction history for undo and rollback.

sysctl reads and writes Linux kernel tunables under /proc/sys. Use sysctl -w for temporary changes, drop files in /etc/sysctl.d/, then sysctl -p or sysctl --system to reload without rebooting — except for parameters that …

On RHEL, Fedora, and related RPM distros, yum and dnf record each install, update, and remove in a SQLite history. Use history list, info, undo, redo, and rollback to reverse transactions — not a substitute for backups …

On RHEL, Rocky Linux, AlmaLinux, and Fedora, grubby is a command-line tool for listing and editing GRUB2 boot entries. It changes default kernels and kernel arguments without hand-editing grub.cfg or running …

Walk a directory tree with grep -r or -R, narrow results with --include and --exclude-dir, and list matching files with -l, -L, and --null. This page covers recursive tree search only — not regex engines or pattern …

SFTP transfers files over SSH. This page covers non-interactive one-liners — URL-style paths, batch files (-b), here-documents, and sshpass patterns — for scripts and cron jobs, not an interactive SFTP shell tutorial.

On RHEL and CentOS, lsyncd watches local directories with inotify and triggers rsync (or rsync over SSH) to mirror changes to another path or host. It is a lightweight live-sync daemon for slowly changing trees.

mount attaches a filesystem (block device, loop file, NFS export, or ISO image) to a directory tree. umount detaches it. fstab lists mounts applied at boot with mount -a.

zip packages and compresses files into a .zip archive. unzip extracts them. Common tasks include recursive directory archives, exclusions, password protection, and listing contents without extracting.

The pssh package provides parallel-ssh, parallel-scp, parallel-slurp, parallel-nuke, and parallel-rsync — Python tools that fan out SSH, copy, and rsync jobs across many hosts from one control node using a host list file …

wget downloads files over HTTP, HTTPS, and FTP without a browser. It supports resume, retries, mirrors, batch URL lists, and quiet automation from scripts and cron jobs.

which reports the pathname of an executable that would run for a given command name, searching directories in PATH in order. It answers which file the shell would start — not whether that file exists on disk in general.

lzop compresses single files with the LZO algorithm and writes .lzo archives. It favors speed over the smallest possible size — useful when you need quick one-file compression without building a tar archive.

xz compresses single files into the .xz format using LZMA2. It replaces the original by default, supports integrity tests, preset levels, and pairs with tar for .tar.xz archives.

bzip2 compresses single files with the Burrows–Wheeler algorithm. By default it replaces the original with a .bz2 file; use -k to keep the source, or pipe to tar for directory archives.

apt-cache reads the local APT package index without network access. Use it to search package names, inspect versions and pinning policy, and trace forward or reverse dependencies before install or removal.

chattr sets filesystem-level attributes on ext2, ext3, and ext4 — immutable (+i) blocks edits and deletion even for root; append-only (+a) allows only adds at the end. Pair it with lsattr to inspect flags before …

ipcs lists System V IPC facilities in the kernel — shared memory segments, message queues, and semaphore arrays. Use it to see what applications allocated, who owns each object, and whether limits are close to …

vmstat prints process, memory, swap, I/O, and CPU activity from /proc. The first sample is often a summary since boot; repeating with a delay shows live trends for quick performance checks.

apt is the high-level package manager on Debian and Ubuntu. It refreshes repository indexes, installs and removes packages with dependency resolution, and queries metadata from configured sources.

chage views and edits password aging fields in /etc/shadow — maximum password age, warning days, inactivity lock, and account expiry. Use it to enforce rotation policy or set temporary accounts without editing shadow by …

chgrp changes the group owner of files and directories without touching the user owner. Use it for shared project trees, web roots, and fixing group mismatches after restores.

usermod changes an existing local user account — login name, UID, primary or supplementary groups, home directory, shell, expiry, and lock state. It edits /etc/passwd, /etc/shadow, /etc/group, and /etc/gshadow.

cat reads files or standard input and writes the bytes to standard output. Use it to view small text files, join files in order, or pipe stdin into a new file with shell redirection.

awk scans input line by line, splits fields, and runs actions when patterns match. Use it to print columns, filter rows, sum numbers, and build quick reports from logs or CSV-style text.

sort reads lines from files or stdin and prints them in order. Use it for log lines, CSV columns, version strings, and pipeline output from ls, awk, or find — then pair with uniq to drop duplicates.

ELinks is a terminal web browser for Linux. It renders pages in text mode for interactive browsing over SSH, and with -dump or -source it prints readable text or raw HTML for scripts and offline docs.

curl transfers data over HTTP, HTTPS, FTP, and other protocols from the shell. Use it to fetch URLs, inspect headers, download files, and send POST and JSON payloads when testing APIs or debugging connectivity.

dumpe2fs prints read-only superblock and block-group metadata for ext2, ext3, and ext4 filesystems. Admins use it to inspect UUIDs, inode counts, mount history, and backup superblock locations before fsck recovery.

locate finds file paths by name using a prebuilt index instead of walking the disk. On Ubuntu 25.04 the locate name is a symlink to plocate; searches are fast but you need updatedb when files were added or removed …