Rohan Timalsina

journalctl reads logs collected by systemd-journald — kernel messages, service output, boot sessions, and syslog traffic in one queryable journal. Filter by unit, time, priority, boot, and process fields without hunting …

nmcli is the command-line client for NetworkManager. It lists devices and connections, sets IPv4/IPv6 addresses, DNS, routes, hostname, and applies profile changes without editing ifcfg files by hand.

Match lines with extended and Perl regex, pattern files, whole words, and context lines on files or stdin. This page covers pattern engines and line-level matching — not recursive directory walks.

mke2fs builds ext2, ext3, or ext4 filesystems on a block device or image file. It is the low-level formatter behind mkfs.ext4 and writes the superblock, inode tables, journal, and default mount metadata for …

losetup attaches regular files or block devices to /dev/loop* kernel nodes so you can partition, format, and mount disk images without dedicated hardware. It also lists, resizes, and detaches loop devices from the shell.

mdadm assembles, creates, monitors, and stops Linux MD RAID devices (md arrays) from partitions or whole disks. It writes version 1.2 metadata superblocks, reports array health, and integrates with /etc/mdadm/mdadm.conf …

pvcreate writes the LVM label and metadata on a disk or partition so it can join a volume group. Use it on empty block devices before vgcreate or vgextend.

vgcfgrestore rebuilds volume group metadata from text backups created by LVM — usually under /etc/lvm/archive and /etc/lvm/backup. It recovers mistyped lvremove or vgcfg changes; it does not replace disk imaging when …

lvscan lists logical volumes on the host with activation state, device path, size, and allocation policy. Use it for a quick inventory before lvdisplay or lvs.

lvdisplay prints detailed logical volume fields — path, UUID, size, extents, allocation, snapshot status, and device-mapper block major:minor. Use it when lvs is not enough.

lvreduce returns free extents from a logical volume to the volume group. Shrink the filesystem first on ext4 — data in the removed region is destroyed. Root LV shrink requires offline maintenance.

lvrename changes the name of a logical volume inside a volume group. The LV UUID and data stay the same — update fstab, boot loaders, and refresh device-mapper after renaming root or data volumes.

lvremove deletes logical volumes from a volume group and frees their extents. Unmount filesystems first — active or open LVs block removal unless you force.

lvchange activates or deactivates logical volumes and updates runtime attributes — read-only access, contiguous allocation, readahead, and metadata refresh after renames.

vgcreate groups one or more physical volumes into a volume group — the storage pool from which logical volumes are allocated. It can initialize PVs automatically if they are not already labeled.

lvcreate allocates logical volumes from free extents in a volume group. Create linear volumes, snapshots, and size-by-percentage LVs before you mkfs and mount.

parted creates and edits partition tables on disks and loop images — GPT or msdos labels, primary and logical partitions, resize, flags, and scripted one-liners. It is the GNU replacement for classic fdisk on large disks …

On RHEL 8+, Fedora, Rocky Linux, and AlmaLinux, dnf is the default RPM package manager. It installs and removes software from repositories, resolves dependencies with libsolv, and keeps a transaction history you can …

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.

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.