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util-linux

util-linux is a diverse collection of userspace utilities essential for system management, encompassing tools for handling file systems, consoles, partitions, messages, and devices. It includes low-level programs necessary for core operating system functions, such as partitioning disks, mounting file systems, and managing processes. Originally developed as part of early distributions, the project was renamed util-linux-ng from 2006 to 2010 to distinguish it from an older version, before reverting to its current name. The package is maintained primarily by Karel Zak and is distributed through the Organization. Key utilities in util-linux cover a wide range of administrative tasks, including for , and umount for operations, for viewing messages, and kill for process signaling. Other notable tools include lsblk for listing devices, hwclock for hardware clock , chrt for scheduling, and uuidgen for generating unique identifiers. The suite also provides libraries like libblkid for device identification and libmount for table , which are used by other system components. As of version 2.41.2, util-linux continues to evolve with updates for modern hardware support and security enhancements, ensuring compatibility across major distributions.

History

Origins and early development

util-linux was founded by Andries E. Brouwer in 1991–1992 as a diverse collection of essential utilities specifically adapted to support the emerging . Brouwer, a and early contributor to the ecosystem, initiated the project to address the need for reliable, low-level tools in the nascent operating system environment. This effort complemented the 's first public release in September 1991 by , providing practical utilities that bridged gaps between the kernel and existing software, thereby enabling a fully functional, non-proprietary system. The initial scope of util-linux focused on delivering core system tools for managing file systems, devices, and basic administration tasks, which were critical for early users lacking comprehensive distribution support. These utilities filled essential voids in the early ecosystem, where developers relied on a patchwork of to achieve operational completeness without depending on proprietary alternatives. By prioritizing compatibility with Unix standards and the evolving , util-linux facilitated hands-on system configuration and maintenance, empowering hobbyists and researchers to experiment with the platform. Among the key early utilities introduced were in 1992 for , and umount in the early 1990s for mounting, and for retrieving ring buffer messages. Fdisk, initially developed with contributions from Brouwer and others, became a cornerstone for creating and manipulating partition tables on hard drives, while /umount handled dynamic attachment of storage devices, and provided vital debugging output from operations. These tools exemplified util-linux's role in enabling practical disk and system management from the outset. A significant milestone occurred by 1993, when util-linux was incorporated into major early Linux distributions such as () and , accelerating its adoption and standardization across the growing user base. This inclusion marked util-linux's transition from a personal project to a foundational component of installations, supporting the rapid expansion of the operating system in academic and enthusiast communities.

Fork and renaming

By the mid-2000s, development of util-linux under its original maintainer, Andries E. Brouwer, and subsequent maintainer Adrian Bunk, had significantly slowed, resulting in a codebase that became increasingly outdated and incompatible with contemporary versions, such as the evolving 2.6 series released in 2003 and subsequent updates. This stagnation left critical utilities, including those for disk management like , unable to fully support new features and device handling requirements, prompting concerns within the community about the project's viability. In response, Karel Zak initiated a known as util-linux-ng ("next generation") on December 18, 2006, branching from the stalled original version 2.13-pre7 to revitalize and modernize the suite. Hosted initially on , the fork aimed to synchronize the utilities with current distributions and kernel developments, while enhancing transparency through Git-based collaboration and a dedicated . Key initial changes included the removal of obsolete components, such as the integrated NFS mounting code (superseded by nfs-utils) and legacy filesystem/device detection routines (replaced by libraries like libblkid from ), streamlining the package for better maintainability. Over the following years, the project adopted autotools for improved build portability across systems. The util-linux-ng era lasted from 2006 to 2010, during which it fostered an active contributor community and prevented the original project's obsolescence. In late 2010, following upstream integration efforts, the fork was officially renamed back to util-linux in January 2011, unifying the lineage and ending the parallel development phase. This transition culminated with version 2.19, released on February 10, 2011, which served as the foundation for all subsequent releases and ensured the suite's continued relevance in ecosystems.

Modern development and releases

Since the leadership transition following the 2006 fork, Karel Zak has served as the primary maintainer of util-linux, leading a collaborative team of contributors under the governance of kernel.org. This structure has enabled steady development, with the project adopting Git for version control in 2006 to manage its codebase through stable branches for releases and the master branch for ongoing enhancements. The project maintains a cadence of major releases approximately every two to three years, alongside minor updates addressing bug fixes and security patches. Notable examples include version 2.20 released in August 2011, 2.30 in 2017, and 2.40 in early 2024, with the latest stable release being 2.41.2 in 2025. In response to evolving features, util-linux has incorporated key adaptations for modern storage and system management. Starting around version 2.20 in 2011 and continuing through subsequent releases, the utility gained enhanced support for filesystems like , including subvolume handling, and improved compatibility for features such as extents and delayed allocation. TRIM support for solid-state drives was introduced via the fstrim utility in version 2.21 (2012), enabling periodic discarding of unused blocks to optimize SSD performance and longevity. Integration with began in earnest around version 2.28 (April 2015), with utilities like sulogin leveraging systemd-run for session management and the package providing systemd unit files, such as fstrim., for automated maintenance tasks. Significant milestones include the addition of the lsblk command in version 2.19 (2011) for listing block devices, which lists active and supports monitoring persistent ones created via bind-mounts to /var/run/netns or similar paths for environments; this was further refined in version 2.35 (January 2020) with improved namespace introspection capabilities. responses have been prompt, as seen in version 2.39 (May 2023), which included patches for vulnerabilities affecting utilities like prlimit, ensuring compatibility with security updates.

Components

Disk and filesystem utilities

The disk and filesystem utilities in util-linux provide essential tools for managing devices, , and filesystems on , enabling administrators to , , probe, and optimize resources. These utilities are critical for system initialization, , and , supporting a wide of from traditional HDDs to modern SSDs and NVMe drives. Developed as part of the util-linux suite, they emphasize reliability and compatibility with the Linux kernel's block layer, often integrating with libraries like libblkid and libmount for enhanced functionality. The and umount commands are foundational for attaching and detaching filesystems to the directory tree, allowing access to device contents. The mount utility, originating in the early as part of initial filesystem management efforts, uses the syntax mount [-t fstype] [-o options] device dir to specify the filesystem type (e.g., ext4 for local journals or NFS for network shares) and mount flags (e.g., noatime to reduce writes for performance). It supports automatic type detection via the and references /etc/[fstab](/page/Fstab) for persistent configurations, requiring root privileges unless user-mounted options are set. Conversely, umount detaches filesystems using umount dir or umount device, ensuring no active processes before unmounting to prevent . Both commands have evolved to handle bind mounts and since util-linux 2.23 in 2014. Partition management is handled by [fdisk](/page/Fdisk) and sfdisk, which manipulate disk labels for creating, resizing, and deleting partitions. fdisk offers an interactive, menu-driven interface for editing MBR () and GPT tables, optimizing alignments for 4K sectors and supporting commands like n to add a new primary partition (e.g., n followed by p for primary, number 1, and +100M for a 100 partition of type 83). It deprecates legacy CHS addressing in favor of modern LBA, making it suitable for interactive administration. In contrast, sfdisk enables scriptable, non-interactive operations, reading partition specifications from stdin (e.g., echo '+100M,' | sfdisk /dev/sda to create a 100 partition) and supporting dump/restore formats for backups. Both tools originated in the under util-linux's early development and now align partitions to device I/O limits by default. For device identification and listing, blkid and lsblk facilitate probing and visualization of block devices. Introduced in the , blkid scans devices for filesystem metadata, outputting attributes like labels and UUIDs (e.g., blkid /dev/sda1 might return TYPE="ext4" UUID="1234-5678"), using libblkid to detect superblocks without mounting. It supports searches by label or UUID (e.g., blkid -L mylabel) and low-level probing to bypass caches. Complementing this, lsblk, added in (version 2.19), lists block devices in a tree-like format (e.g., showing /dev/sda with children /dev/sda1), drawing from and for details on mounts, sizes, and types, excluding RAM disks by default. These tools aid in modern storage setups by ignoring private LVM devices since util-linux 2.25. Additional utilities address specialized needs, such as optimization and cleanup. fstrim, designed for SSD maintenance, issues commands to discard unused blocks on mounted filesystems (e.g., fstrim -v / reports trimmed bytes), improving performance and longevity on thinly-provisioned ; it supports all entries via -a and was enhanced for broader handling in util-linux 2.25. wipefs clears filesystem or partition signatures (e.g., wipefs -a /dev/sda erases all magic strings without data loss), making devices appear blank to libblkid and notifying the via for repartitioning. findfs locates devices by tag (e.g., findfs UUID=1234-5678 outputs /dev/sda1), leveraging blkid for quick resolution in scripts or mounts. Since 2.25 in 2014, these tools have incorporated support for advanced features like LVM private device filtering through updated libblkid and integrations, adapting to evolving technologies.

Process and user management utilities

The process and user management utilities in util-linux form a core set of tools for managing identities, sessions, inter-user communication, process termination, and login auditing in multi-user systems. These utilities support secure authentication through integration with the Pluggable Authentication Modules () framework and enable administrators to control access and monitor activity effectively. Originating from early Unix traditions and incorporated into util-linux during its foundational development in the , these tools have evolved to leverage modern features like capabilities and namespaces for enhanced security and isolation. The command facilitates switching to another user account, defaulting to root, and prompts for the target user's password unless executed by root. With the -l (or --login) option, it initializes a complete login environment, including the user's , , and variables, simulating a full . Su has in Unix systems from the but became a standard component of util-linux in the , with modern implementations relying on for flexible authentication since the early to handle password verification, session setup, and logging. Similarly, the utility authenticates users during console or network sessions, reading credentials from /etc/passwd and invoking PAM modules for validation, environment setup, and resource limits. It supports options like -f for automatic login without password prompts in trusted scenarios and records session details in /var/log/wtmp for auditing. Like su, login traces its origins to early Unix but was integrated into util-linux in the 1990s, with PAM support added in the 2000s to enable pluggable backends for authentication, such as LDAP or . For inter-user communication, broadcasts a to all logged-in users across s, padding short lines to 79 characters and appending a header indicating the sender. It is commonly used by administrators for announcements, such as system maintenance notices, and can read input from a file or standard input. The write command, in contrast, targets a specific user by username or terminal, enabling direct chat-like interactions but respecting the recipient's permissions. Both tools, part of util-linux since its early releases, rely on /utmpx files to identify active sessions and are essential for collaborative system administration. The kill utility sends signals to processes by or job number, with SIGTERM (signal 15) as the default for requesting graceful termination; options like -9 invoke SIGKILL for forceful stops. It supports job control in interactive shells and can target process groups with - prefix. Included in util-linux from its inception in the , kill provides a low-level for process management, often combined with tools like [ps](/page/PS) for identification. Additional utilities include last, which displays historical login sessions from /var/log/wtmp, showing , , duration, and timestamps to aid in auditing access patterns. The mesg command controls write permissions on a user's , allowing or denying incoming messages from write or with mesg y or mesg n, enhancing in shared environments. These tools have been core to util-linux since the , supporting system monitoring without requiring elevated privileges beyond basic file access. Security enhancements in these utilities include integration with Linux capabilities and namespaces, notably via unshare (introduced around 2010), with enhancements in util-linux version 2.27 in 2015. Unshare runs a program in a new (e.g., , , or ) for isolation, with options like --user or --pid to detach from the parent's ; since version 2.27, it automatically sets propagation to private to prevent shared mounts. This supports container-like environments and privilege reduction, complementing PAM-based authentication in tools like and for robust .

System information and monitoring utilities

The system information and monitoring utilities in util-linux provide read-only interfaces for inspecting messages, configurations, user activities, and resource allocations, facilitating diagnostics and without modifying system state. These tools draw from kernel interfaces like /proc, , and log files to deliver structured output, often with customizable formats for scripting or analysis. dmesg examines and controls the ring , displaying diagnostic messages generated during boot and runtime events such as hardware initialization or errors. By default, it prints all available messages, but options like --clear empty the after display, while -T adds human-readable timestamps derived from the (RTC) or monotonic clock for chronological context. Introduced in the early as a core aid in early distributions, remains essential for analyzing -level issues. Recent enhancements, such as the --follow-new option added in version 2.36 (2021), enable monitoring by waiting for and printing only subsequent messages, improving its utility for ongoing diagnostics. lscpu queries and formats CPU architecture details, including type, number of cores, threads, clock speed, and feature flags such as avx2 for instructions or support. It aggregates data from /proc/cpuinfo, , and architecture-specific libraries, presenting it in a tabular or parsable format via options like -J for output. Added to util-linux in version 2.15 (around 2009) to provide a standardized view beyond raw /proc data, lscpu has evolved with multi-architecture support; for instance, version 2.32 (2018) introduced userspace decoding for CPUs to handle kernel limitations in /proc/cpuinfo readability. lslogins compiles and displays user account summaries, integrating data from /etc/, /etc/, wtmp, btmp, and faillog files to show login histories, last access times, failed attempts, and /GID mappings. Options like -u filter by user, while -i includes inode information for associated files. Inspired by FreeBSD's logins utility but tailored for , lslogins was introduced in version 2.23 (April 2014) to streamline security audits and user management queries. Additional tools extend monitoring capabilities: lsirq, added in version 2.36 (2021), lists (IRQ) counters with sortable columns for IRQ number, device, and counts, aiding in identifying bottlenecks. fuser identifies associated with files, points, or sockets, offering lsof-like functionality focused on process IDs and access types (e.g., read/write/execute), with the -k option to terminate them; it scans /proc for efficiency and supports verbose output for file locks. Util-linux has adapted these utilities for modern environments, including ; version 2.36 (2021) incorporated support for cgroup v2 hierarchies in relevant tools, ensuring compatibility with the latest features for isolated .

Miscellaneous system utilities

The miscellaneous system utilities in util-linux encompass a collection of tools that handle general system administration tasks, including swap space management, clock operations, command-line option parsing, file locking, configuration, and UUID generation. These utilities provide essential functionality for system maintenance and scripting, often invoked during processes or in administrative scripts. They have evolved to support modern features while maintaining compatibility with legacy behaviors. The swapon and swapoff utilities manage swap space by enabling or disabling paging and swapping on devices or files. Swapon activates swap areas, typically during system initialization to distribute memory pressure across multiple partitions or files, and supports options for specifying levels (ranging from -1 for lowest to 32767 for highest) to influence which swap space is used first by the . Swapoff deactivates specified or all swap areas, useful for maintenance or reconfiguration, and can discard data if the device supports it. These tools, originating from 4.0BSD practices, have been core components of util-linux since the , predating widespread adoption of dynamic filesystems. Hwclock interfaces with the clock (, or ) to display, set, or synchronize time between the and the system clock. It handles conversions between UTC and zones, using the /etc/adjtime to track drift factors and timescale preferences, and applies to account for systematic inaccuracies in the . For instance, the --systohc option sets the from the system time, while --hctosys does the reverse, often automated in boot scripts. Originally derived from the clock developed in 1996, hwclock underwent significant refinements starting in version 2.26 (2015), including automatic drift compensation and removal of obsolete ISA bus fallbacks to align with contemporary . Getopt parses command-line s in shell scripts, supporting both short options (e.g., -a) and long options (e.g., --all), along with required or optional parameters, to facilitate robust option handling without string processing. It outputs reformatted s in a quoted format to preserve spaces and special characters, making it a staple for scripting in util--based systems. The util- implementation, enhanced from earlier BSD versions, includes long option support as a key feature for compliance and GNU-style parsing, with refinements in version 2.30 (2017) improving compatibility and error reporting for complex lists. Additional utilities include [flock](/page/Flock), which applies advisory locks to files or directories using the flock(2) system call, enabling scripts to coordinate access and prevent concurrent modifications—commonly used with options like -x for exclusive locks or -n for non-blocking attempts. Setterm configures terminal attributes, such as foreground/background colors, cursor visibility, screen blanking timeouts (up to 60 minutes), and bell frequencies for virtual consoles, outputting terminfo-compatible escape sequences for precise control. Uuidgen generates RFC 4122-compliant UUIDs, defaulting to random variants but supporting time-based, , or hashing with namespace inputs for deterministic outputs in applications like filesystem labeling. Post-2010 developments integrated libudev support into select util-linux tools, such as lsblk and findmnt, allowing them to monitor device events and query udev-managed properties for dynamic hardware handling without direct access. In 2015, legacy elements like the original clock command's direct ISA modes were deprecated in favor of streamlined interfaces, reflecting a shift toward modern embedded and virtualized environments.

Licensing and distribution

License structure

The util-linux project utilizes a multi-license framework, with the majority of its code governed by licenses to ensure openness while accommodating varied use cases across components. Executables such as are primarily licensed under the version 2 or later (GPL-2.0-or-later), promoting strong requirements for derivative works. Libraries, including libmount, fall under the GNU Lesser General Public License version 2.1 or later (LGPL-2.1-or-later), which permits linking with without imposing full on the entire application. Certain utilities, like hexdump, employ permissive , such as BSD-2-Clause or BSD-3-Clause, allowing broader reuse with fewer restrictions. The project's licensing evolved from its origins in the , when initial code developed by Andries Brouwer was released in the , lacking formal restrictions. Following the 2006 fork into util-linux-ng (later renamed back to util-linux) led by Karel Zak due to stalled maintenance, the licenses were standardized to GPL-2.0-or-later and LGPL-2.1-or-later for most components, enhancing protections and aligning with principles. Some elements retained status or adopted permissive licenses during this transition. Licenses vary by file and component within the ; for instance, files are typically under GPL-3.0-or-later, while select header files use BSD-3-Clause. Comprehensive on per-file licensing, including all applicable variants like and , are documented in the project's README.licensing file. This structure enables free redistribution, modification, and use of util-linux components in open-source projects, but GPL-covered portions mandate availability in distributions and prohibit proprietary derivatives without relicensing. LGPL components offer more flexibility for integration into closed-source applications. No proprietary forks are feasible under the terms without explicit relicensing approval. License compliance is upheld through official releases hosted on , with the addition of identifiers beginning in version 2.35 (released in 2020) to standardize and automate license detection across files.

Integration in Linux distributions

Util-linux is a standard component in nearly all distributions, with packages available in over 900 repositories across major ecosystems. For instance, packages util-linux as a that builds into multiple packages, including the core util-linux for miscellaneous utilities, bsdutils for basic BSD-derived tools like kill and ps, and components supporting wall for broadcasting messages, ensuring modular installation based on user needs. This structure aligns versions with releases to maintain compatibility during and management tasks. Packaging variations exist to suit distribution philosophies. In , util-linux is split into modular components such as libsmartcols for formatting libraries used in tools like lsblk, alongside separate packages for libmount and libblkid, facilitating selective dependency management in modular environments. , meanwhile, provides development headers through packages like libblkid-dev and libfdisk-dev, enabling compilation of applications that link against util-linux libraries without installing the full suite. Version syncing differs by distribution priorities. Rolling-release distros like closely track upstream releases, incorporating version 2.41.2 in their 2025 repositories shortly after the September 2025 upstream v2.41 announcement. In contrast, enterprise distributions such as (RHEL) 8 prioritize stability, retaining version 2.32.1 to avoid disruptions in production environments. Distributions often introduce customizations for integration. For example, systemd's mount units provide a declarative mounting mechanism that can override or complement the traditional mount command from util-linux, allowing automated handling of filesystems during boot via .mount files. Historically, components like BSD-derived utilities have been split into separate packages, such as bsdextrautils in , to reduce the core footprint and align with licensing or modularity goals. The package's impact is profound in system initialization, as it supplies critical tools for boot processes; initramfs images commonly include for management and for filesystem attachment, enabling the to access the root filesystem before full userland loading. This ubiquity underscores util-linux's role as foundational infrastructure across ecosystems.

Development and maintenance

Project governance

The util-linux project is led by principal maintainer Karel Zak, who has overseen development since forking the original codebase into util-linux-ng in December 2006, later reverting to the util-linux name in 2010. While Zak handles core oversight and sensitive bug reports as a software engineer, subsystem-specific contributions, such as those for disk utilities, are managed by dedicated developers who review and integrate patches. Project decisions are made collaboratively through discussions on the util-linux@vger. and direct commits to the repository, ensuring transparency in the approval process. The source code is hosted at (established 1995) under the Linux Kernel Organization (established 2002), and has been maintained in a repository at git.kernel.org/pub/scm/utils/util-linux/util-linux.git, which serves as the official upstream for distributions worldwide. Community involvement extends to internationalization efforts via the Translation Project, supporting translations in 43 languages as of November 2025, with 12 fully translated (e.g., , , ) and PO files integrated directly into the repository for ongoing maintenance. Development policies emphasize a pragmatic approach: the master branch operates under an "it works for me" status, indicating functional but potentially untested changes suitable for bleeding-edge use, while stable branches (e.g., stable/v2.41) are frozen post-release for bug fixes only. Deprecations follow a structured announcement process, with removals of obsolete tools previewed in release notes; for instance, the 2.27 release in November 2015 deprecated commands like tailf (in favor of coreutils) and mkfs (replaced by type-specific variants), with prior warnings issued in earlier changelogs to allow community adaptation over several months. Sustainability relies on the broader community without a dedicated formal foundation, drawing support from employer sponsorships like for maintainer time and infrastructure provided by the , which hosts and facilitates participation in events such as LinuxCon.

Contribution and reporting processes

Individuals can report bugs in util-linux by submitting issues on the project's GitHub repository at github.com/util-linux/util-linux or by emailing the mailing list at [email protected]. Issues are triaged by project maintainers, who prioritize and assign them based on severity and impact. For sensitive security issues, contributors are advised to contact the lead maintainer, Karel Zak, privately at [email protected] before public disclosure to allow for coordinated response, aligning with practices similar to those in the community. Code contributions are submitted as pull requests on GitHub or as patches via the mailing list, with the primary repository hosted at git.kernel.org/pub/scm/utils/util-linux/util-linux.git. Contributors must follow the Linux kernel coding style, which emphasizes 8-character indents, 80-column line limits, and specific brace placement, while ensuring compliance with C standards such as C99 for portability. Patches should be small, focused on a single logical change, and include a Signed-off-by line; they undergo review by maintainers, requiring sign-off before merging. Man pages must adhere to standard formats, preserving existing options and maintaining Open Group specifications for core utilities like cal and kill. Translations are handled through the Translation Project at translationproject.org/domain/util-linux.html, where volunteers update PO files based on the latest POT template, such as util-linux-2.41.2-rc1.pot. Updates are submitted via team-specific email lists, and integrated PO files are included in upstream releases; as of 2025, full translations (100% complete) are available for and , while stands at approximately 99% completeness. Testing is encouraged through the project's autotools-based suite, invoked via make check after building, which runs regression tests in the tests/ directory covering utilities across architectures like x86 and . Contributors are urged to verify patches do not introduce on their platforms and to report any failures to the mailing list for broader validation. New contributors face barriers such as mastering the coding style and navigating the patch review process, but are recommended to begin with low-risk tasks like documentation fixes or minor man-page updates before tackling changes. Under , these processes ensure maintainability while fostering community involvement.