OpenSSL guide (opens in a new tab)
A structured introduction to the toolkit, its libraries, providers, and application development.
OpenSSL Project · docs.openssl.org
OpenSSL 3.5
Foundations
A working reference for Linux
The complete collection.
Selected documentation for Linux system administrators and software engineers. Find the right manual, understand the tool, and get back to work.
48References
8Topics
TLS concepts and protocol versions (opens in a new tab)
Understand encryption, peer authentication, and protocol negotiation before debugging a TLS connection.
OpenSSL Project · docs.openssl.org
OpenSSL 3.5
Foundations
s_client: diagnose TLS connections (opens in a new tab)
Inspect handshakes, SNI, certificate chains, and hostname verification using the command-line client.
OpenSSL Project · docs.openssl.org
OpenSSL 3.5
Diagnostics
x509: inspect and process certificates (opens in a new tab)
Look up certificate fields, expiry dates, extensions, fingerprints, and encoding conversions.
OpenSSL Project · docs.openssl.org
OpenSSL 3.5
Certificates
verify: certificate chain validation (opens in a new tab)
Understand trust stores, chain building, verification purposes, and certificate validation failures.
OpenSSL Project · docs.openssl.org
OpenSSL 3.5
Certificates
OpenSSH manual collection (opens in a new tab)
The upstream starting point for SSH clients, daemons, agents, keys, and file-transfer tools.
OpenSSH Project · openssh.org
Upstream manuals; features may precede Linux packages
Overview
ssh: connections and forwarding (opens in a new tab)
Look up remote commands, jump hosts, multiplexing, and local or remote port forwarding.
OpenBSD / OpenSSH · man.openbsd.org
OpenBSD current; compare installed OpenSSH
Client & server
ssh_config: client configuration (opens in a new tab)
Configure host aliases, identities, connection behavior, and matching rules for repeatable access.
OpenBSD / OpenSSH · man.openbsd.org
OpenBSD current; compare installed OpenSSH
Client & server
sshd_config: server configuration (opens in a new tab)
Check authentication, access controls, subsystems, and conditional server configuration.
OpenBSD / OpenSSH · man.openbsd.org
OpenBSD current; compare installed OpenSSH
Client & server
ssh-keygen: keys and SSH certificates (opens in a new tab)
Generate and inspect keys, manage known hosts, and understand SSH certificate operations.
OpenBSD / OpenSSH · man.openbsd.org
OpenBSD current; compare installed OpenSSH
Keys & transfers
sftp: secure file transfer (opens in a new tab)
Reference interactive and batch transfer commands, path handling, and connection options.
OpenBSD / OpenSSH · man.openbsd.org
OpenBSD current; compare installed OpenSSH
Keys & transfers
Filesystem Hierarchy Standard (opens in a new tab)
The standard for directory placement and the roles of /etc, /var, /usr, /opt, and /run.
Linux Foundation · refspecs.linuxfoundation.org
FHS 3.0 (2015); distributions may use merged /usr
Layout & concepts
How Linux resolves a pathname (opens in a new tab)
Follow path traversal, symbolic links, permissions, and mount boundaries.
Linux man-pages / util-linux · man7.org
Current upstream manual; compare installed version
Layout & concepts
Inodes, ownership, and permissions (opens in a new tab)
Understand file metadata, link counts, timestamps, ownership, and access mode bits.
Linux man-pages / util-linux · man7.org
Current upstream manual; compare installed version
Layout & concepts
mount: filesystem attachment and options (opens in a new tab)
Reference mount options, bind mounts, propagation, and filesystem-specific behavior.
Linux man-pages / util-linux · man7.org
Current upstream manual; compare installed version
Mounts
findmnt: inspect mounted filesystems (opens in a new tab)
Find a mount by path, device, label, or UUID and choose explicit output columns.
Linux man-pages / util-linux · man7.org
Current upstream manual; compare installed version
Mounts
Linux kernel filesystem documentation (opens in a new tab)
Explore VFS, filesystem implementations, and the interfaces behind userspace storage tools.
Linux Kernel · docs.kernel.org
Current upstream kernel documentation
Kernel internals
Bash reference manual (opens in a new tab)
Understand quoting, expansion, redirection, pipelines, shell functions, and scripting semantics.
GNU Project · gnu.org
Maintained GNU manual; compare installed version
Shell
GNU Coreutils manual (opens in a new tab)
The comprehensive reference for everyday file, text, permission, and system utilities.
GNU Project · gnu.org
Maintained GNU manual; compare installed version
Files & archives
GNU Findutils manual (opens in a new tab)
Find files by metadata and compose robust find, xargs, and locate workflows.
GNU Project · gnu.org
Maintained GNU manual; compare installed version
Files & archives
GNU tar manual (opens in a new tab)
Create, inspect, and extract archives; understand names, metadata, and incremental archive behavior.
GNU Project · gnu.org
Maintained GNU manual; compare installed version
Files & archives
GNU sed manual (opens in a new tab)
Learn stream editing, substitutions, address ranges, and pattern-space operations.
GNU Project · gnu.org
Maintained GNU manual; compare installed version
Text processing
GNU awk manual (opens in a new tab)
Work with records, fields, patterns, associative arrays, and text-processing programs.
GNU Project · gnu.org
Maintained GNU manual; compare installed version
Text processing
Everything curl (opens in a new tab)
A book by curl’s founder and contributors covering the tool, protocols, and library.
curl Project · everything.curl.dev
Current curl documentation; check local curl version
Getting started
curl command-line tutorial (opens in a new tab)
Learn transfer workflows, authentication, proxies, uploads, and practical command-line options.
curl Project · curl.se
Current curl documentation; check local curl version
Getting started
curl option reference (opens in a new tab)
Look up flags, exit codes, protocol behavior, and the versions in which options appeared.
curl Project · curl.se
Current curl documentation; check local curl version
HTTP & TLS
Scripting HTTP requests (opens in a new tab)
Build requests with forms, POST bodies, cookies, redirects, and authentication.
curl Project · curl.se
Current curl documentation; check local curl version
HTTP & TLS
TLS certificate verification in curl (opens in a new tab)
Understand CA stores, native trust, certificate verification, and custom trust configuration.
curl Project · curl.se
Current curl documentation; check local curl version
HTTP & TLS
libcurl programming tutorial (opens in a new tab)
Integrate transfers with the C API, callbacks, handles, and error handling.
curl Project · curl.se
Current curl documentation; check local curl version
Development
Regular expressions in GNU grep (opens in a new tab)
Compare basic, extended, and Perl-compatible expressions and understand matching behavior.
GNU Project · gnu.org
GNU grep; BRE, ERE, and PCRE modes differ
POSIX & GNU
POSIX regular expression specification (opens in a new tab)
The normative definitions of basic and extended regular expressions, including locale behavior.
The Open Group / IEEE · pubs.opengroup.org
POSIX.1-2024, Base Definitions chapter 9
POSIX & GNU
Regular expressions in awk (opens in a new tab)
Apply patterns in awk and understand operators, escapes, and dynamic regular expressions.
GNU Project · gnu.org
GNU awk; ERE with documented extensions
POSIX & GNU
PCRE2 pattern reference (opens in a new tab)
Explore captures, lookarounds, Unicode properties, backtracking, and advanced pattern semantics.
PCRE2 Project · pcre.org
Current PCRE2 documentation
PCRE2
PCRE2 syntax quick reference (opens in a new tab)
A compact syntax reference for metacharacters, character classes, groups, and assertions.
PCRE2 Project · pcre.org
Current PCRE2 documentation
PCRE2
Debian package management handbook (opens in a new tab)
Understand APT and dpkg, package states, dependencies, upgrades, and repository priorities.
Debian Project · debian.org
Maintained Debian Reference; Debian-based systems
Debian & Ubuntu
apt: interactive package management (opens in a new tab)
Reference package installation, removal, searches, and upgrades for interactive administration.
Debian Project · manpages.debian.org
Debian 13 trixie; use apt-get for stable scripting interfaces
Debian & Ubuntu
APT repository authentication (opens in a new tab)
Understand signed repository metadata, trusted keys, and the archive authentication model.
Debian Project · manpages.debian.org
Debian 13 trixie / APT
Debian & Ubuntu
DNF5 documentation (opens in a new tab)
Find commands for package transactions, repositories, queries, and transaction history.
DNF Project · dnf5.readthedocs.io
DNF5 latest; DNF4 has a separate interface
Fedora & RPM
RPM documentation (opens in a new tab)
Select the matching RPM manual for package queries, verification, and package-building concepts.
RPM Project · rpm.org
Versioned RPM manuals; choose the installed release
Fedora & RPM
zypper: packages and repositories (opens in a new tab)
Manage packages and repositories, inspect dependencies, and understand updates, patches, and distribution upgrades.
openSUSE Project · manpages.opensuse.org
openSUSE Leap 16.0 manual
openSUSE
pacman command reference (opens in a new tab)
Inspect package databases and understand synchronization, queries, upgrades, and removals.
Arch Linux / pacman · pacman.archlinux.page
Current pacman manual
Arch Linux
ip: interfaces, addresses, and routes (opens in a new tab)
Navigate iproute2 objects for links, addresses, routes, policy rules, and network namespaces.
iproute2 / man7.org · man7.org
Current iproute2 manual
Interfaces & routes
ss: sockets and connections (opens in a new tab)
Inspect listening ports, socket states, process associations, and protocol statistics.
iproute2 / man7.org · man7.org
Current iproute2 manual
Sockets & packets
dig and BIND 9 utilities (opens in a new tab)
Query DNS records and authoritative servers using the BIND manual’s dig reference.
ISC BIND · bind9.readthedocs.io
BIND 9 stable documentation
DNS
nftables project handbook (opens in a new tab)
Learn tables, chains, hooks, sets, and packet-filtering rules from the Netfilter project.
Netfilter Project · wiki.nftables.org
Maintained nftables wiki
Firewall & kernel
tcpdump packet capture manual (opens in a new tab)
Reference capture interfaces, packet output, filters, and save-file handling.
The Tcpdump Group · tcpdump.org
Current tcpdump manual
Sockets & packets
nmcli: NetworkManager CLI (opens in a new tab)
Inspect devices and connection profiles and understand NetworkManager command behavior.
NetworkManager Project · networkmanager.dev
Latest NetworkManager manual
Interfaces & routes
Linux IP sysctl reference (opens in a new tab)
Understand the kernel’s IPv4, IPv6, and transport configuration parameters.
Linux Kernel · docs.kernel.org
Current upstream kernel; options depend on kernel version
Firewall & kernel