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SystemD Usage Guide

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  • Systemd Usage Guide on RHEL 7

    i | P a g e

    Table of Contents Overview ....................................................................................................................................................... 1

    Applies To .................................................................................................................................................. 1

    Pre-Requisites ........................................................................................................................................... 1

    Systemd Generic Information .................................................................................................................... 1

    Version ...................................................................................................................................................... 1

    Binaries...................................................................................................................................................... 1

    Process System.......................................................................................................................................... 2

    Systemd Units ............................................................................................................................................ 2

    Systemd Boot Process ................................................................................................................................ 3

    Analyze systemd Boot Process ............................................................................................................... 3

    Analyze systemd Each Boot Process ...................................................................................................... 4

    Analyze systemd Critical Chain at Boot .................................................................................................. 5

    Analyze systemd Critical Chain by Service Unit ..................................................................................... 6

    Analyze systemd Critical Chain by Target .............................................................................................. 6

    Systemd Units Commands ............................................................................................................................ 7

    List Units Available ................................................................................................................................. 7

    List Units Running .................................................................................................................................. 8

    List Units Failed ...................................................................................................................................... 8

    List Units By Type Service ....................................................................................................................... 9

    List Units By Type Mount ....................................................................................................................... 9

    List Units By Type Socket ..................................................................................................................... 10

    List Units By Type Slice ......................................................................................................................... 10

    List Units By Type Swap........................................................................................................................ 11

    List Units By Type Snapshot ................................................................................................................. 11

    List Units By Type Path ......................................................................................................................... 11

    List Units By Type Timer ....................................................................................................................... 12

    So Whats systemctl / systemd unit Files .................................................................................................... 12

    List Service All Properties ..................................................................................................................... 13

    List Service Specific Property - CPUShares ........................................................................................... 13

    List Service Specific Property - CanReload ........................................................................................... 14

    List Service Specific Property - Conflicts .............................................................................................. 14

  • Systemd Usage Guide on RHEL 7

    ii | P a g e

    Service Dependencies ................................................................................................................................. 14

    List Dependencies ................................................................................................................................... 15

    List Service Dependencies by Service ..................................................................................................... 16

    List Dependencies by Target ................................................................................................................... 16

    List Service Dependencies For Service ................................................................................................. 17

    List Service Dependencies Before ........................................................................................................ 17

    List Service Dependencies After ........................................................................................................... 18

    List Service Dependencies Reverse ...................................................................................................... 18

    List Service Dependencies Target ........................................................................................................ 19

    List Service Dependencies Plot ............................................................................................................ 19

  • Systemd Usage Guide on RHEL 7

    1 | P a g e

    Overview

    Systemctl is a systemd utility which is responsible for controlling the systemd system and service manager.

    Systemd is a collection of system management daemons, utilities and libraries which serves as a

    replacement of SystemV init daemon.

    Systemd functions as central management and configuration platform for UNIX like system.

    Applies To

    Tested on RHEL 7, CentOS 7.

    Pre-Requisites

    None

    Systemd Generic Information

    Version

    To find the version of systemctl executable, run the command;

    systemctl --version

    Binaries

    To find the binaries of systemctl executable, run the command;

    whereis systemctl

  • Systemd Usage Guide on RHEL 7

    2 | P a g e

    Process System

    To know the process associated with systemd run the command;

    ps -eaf | grep [s]ystemd

    Systemd Units

    There are different units that are managed by systemd and it accepts following units.

    Systemctl Units Purpose

    systemd.service Manage System Service; A unit configuration file whose name ends in .service encodes information about a process controlled and supervised by systemd.

    systemd.socket Manage sockets for each service; A unit configuration file whose name ends in ".socket" encodes information about an IPC or network socket or a file system FIFO controlled and supervised by systemd, for socket-based activation.

    systemd.device Manage devices; A unit configuration file whose name ends in ".device" encodes information about a device unit as exposed in the sysfs/udev device tree.

    systemd.mount Manage mount points; A unit configuration file whose name ends in ".mount" encodes information about a file system mount point controlled and supervised by systemd.

    systemd.target Manage targets; A unit configuration file whose name ends in ".target" encodes information about a target unit of systemd, which is used for grouping units and as well-known synchronization points during start-up. Target units do not offer any additional functionality on top of the generic functionality provided by units. They exist merely to group units via dependencies (useful as boot targets), and to establish standardized names for synchronization points used in dependencies between units. Among other

  • Systemd Usage Guide on RHEL 7

    3 | P a g e

    things, target units are a more flexible replacement for SysV runlevels in the classic SysV init system.

    systemd.paths Check the existence of files or directories or create them as needed

    systemd.slices Manage resources

    systemd.snapshots Takes snapshots of the current state of the system

    systemd.sockets Set up sockets to allow communication paths to processes that can remain in place, even if the underlying process needs to restart

    systemd.swaps Create and use swap files or swap partitions

    Systemd.timer Trigger actions based on a timer

    Systemd Boot Process

    systemd is the first process started by the kernel. It replaces the venerable SysVinit program (also

    called init) and the newer Upstart init system. systemd coordinates the rest of the boot process and

    configures the environment for the user.

    systemd improves on other init systems with increased parallelization. It

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