systemd/README

systemd System and Service Manager

DETAILS:
        http://0pointer.de/blog/projects/systemd.html

WEB SITE:
        https://www.freedesktop.org/wiki/Software/systemd

GIT:
        git@github.com:systemd/systemd.git
        https://github.com/systemd/systemd.git

GITWEB:
        https://github.com/systemd/systemd

MAILING LIST:
        https://lists.freedesktop.org/mailman/listinfo/systemd-devel

IRC:
        #systemd on irc.freenode.org

BUG REPORTS:
        https://github.com/systemd/systemd/issues

AUTHOR:
        Lennart Poettering
        Kay Sievers
        ...and many others

LICENSE:
        LGPLv2.1+ for all code
        - except src/basic/MurmurHash2.c which is Public Domain
        - except src/basic/siphash24.c which is CC0 Public Domain
        - except src/journal/lookup3.c which is Public Domain
        - except src/udev/* which is (currently still) GPLv2, GPLv2+

REQUIREMENTS:
        Linux kernel >= 3.13
        Linux kernel >= 4.2 for unified cgroup hierarchy support

        Kernel Config Options:
          CONFIG_DEVTMPFS
          CONFIG_CGROUPS (it is OK to disable all controllers)
          CONFIG_INOTIFY_USER
          CONFIG_SIGNALFD
          CONFIG_TIMERFD
          CONFIG_EPOLL
          CONFIG_NET
          CONFIG_SYSFS
          CONFIG_PROC_FS
          CONFIG_FHANDLE (libudev, mount and bind mount handling)

        Kernel crypto/hash API
          CONFIG_CRYPTO_USER_API_HASH
          CONFIG_CRYPTO_HMAC
          CONFIG_CRYPTO_SHA256

        udev will fail to work with the legacy sysfs layout:
          CONFIG_SYSFS_DEPRECATED=n

        Legacy hotplug slows down the system and confuses udev:
          CONFIG_UEVENT_HELPER_PATH=""

        Userspace firmware loading is not supported and should
        be disabled in the kernel:
          CONFIG_FW_LOADER_USER_HELPER=n

        Some udev rules and virtualization detection relies on it:
          CONFIG_DMIID

        Support for some SCSI devices serial number retrieval, to
        create additional symlinks in /dev/disk/ and /dev/tape:
          CONFIG_BLK_DEV_BSG

        Required for PrivateNetwork= and PrivateDevices= in service units:
          CONFIG_NET_NS
          CONFIG_DEVPTS_MULTIPLE_INSTANCES
        Note that systemd-localed.service and other systemd units use
        PrivateNetwork and PrivateDevices so this is effectively required.

        Required for PrivateUsers= in service units:
          CONFIG_USER_NS

        Optional but strongly recommended:
          CONFIG_IPV6
          CONFIG_AUTOFS4_FS
          CONFIG_TMPFS_XATTR
          CONFIG_{TMPFS,EXT4,XFS,BTRFS_FS,...}_POSIX_ACL
          CONFIG_SECCOMP
          CONFIG_SECCOMP_FILTER (required for seccomp support)
          CONFIG_CHECKPOINT_RESTORE (for the kcmp() syscall)

        Required for CPUShares= in resource control unit settings
          CONFIG_CGROUP_SCHED
          CONFIG_FAIR_GROUP_SCHED

        Required for CPUQuota= in resource control unit settings
          CONFIG_CFS_BANDWIDTH

        For UEFI systems:
          CONFIG_EFIVAR_FS
          CONFIG_EFI_PARTITION

        We recommend to turn off Real-Time group scheduling in the
        kernel when using systemd. RT group scheduling effectively
        makes RT scheduling unavailable for most userspace, since it
        requires explicit assignment of RT budgets to each unit whose
        processes making use of RT. As there's no sensible way to
        assign these budgets automatically this cannot really be
        fixed, and it's best to disable group scheduling hence.
           CONFIG_RT_GROUP_SCHED=n

        Note that kernel auditing is broken when used with systemd's
        container code. When using systemd in conjunction with
        containers, please make sure to either turn off auditing at
        runtime using the kernel command line option "audit=0", or
        turn it off at kernel compile time using:
          CONFIG_AUDIT=n
        If systemd is compiled with libseccomp support on
        architectures which do not use socketcall() and where seccomp
        is supported (this effectively means x86-64 and ARM, but
        excludes 32-bit x86!), then nspawn will now install a
        work-around seccomp filter that makes containers boot even
        with audit being enabled. This works correctly only on kernels
        3.14 and newer though. TL;DR: turn audit off, still.

        glibc >= 2.16
        libcap
        libmount >= 2.27.1 (from util-linux)
                (util-linux *must* be built with --enable-libmount-force-mountinfo)
        libseccomp >= 2.3.1 (optional)
        libblkid >= 2.24 (from util-linux) (optional)
        libkmod >= 15 (optional)
        PAM >= 1.1.2 (optional)
        libcryptsetup (optional)
        libaudit (optional)
        libacl (optional)
        libselinux (optional)
        liblzma (optional)
        liblz4 >= 119 (optional)
        libgcrypt (optional)
        libqrencode (optional)
        libmicrohttpd (optional)
        libpython (optional)
        libidn (optional)
        elfutils >= 158 (optional)
        make, gcc, and similar tools

        During runtime, you need the following additional
        dependencies:

        util-linux >= v2.27.1 required
        dbus >= 1.4.0 (strictly speaking optional, but recommended)
                NOTE: If using dbus < 1.9.18, you should override the default
                policy directory (--with-dbuspolicydir=/etc/dbus-1/system.d).
        dracut (optional)
        PolicyKit (optional)

        When building from git, the following tools are needed:

        pkg-config
        docbook-xsl
        xsltproc
        automake
        autoconf
        libtool
        intltool
        gperf
        python (optional)
        python-lxml (optional, but required to build the indices)

        The build system is initialized with ./autogen.sh. A tar ball
        can be created with:
          git archive --format=tar --prefix=systemd-222/ v222 | xz > systemd-222.tar.xz

        When systemd-hostnamed is used, it is strongly recommended to
        install nss-myhostname to ensure that, in a world of
        dynamically changing hostnames, the hostname stays resolvable
        under all circumstances. In fact, systemd-hostnamed will warn
        if nss-myhostname is not installed.

        Additional packages are necessary to run some tests:
        - busybox            (used by test/TEST-13-NSPAWN-SMOKE)
        - nc                 (used by test/TEST-12-ISSUE-3171)
        - python3-pyparsing
        - python3-evdev      (used by hwdb parsing tests)
        - strace             (used by test/test-functions)
        - capsh              (optional, used by test-execute)

USERS AND GROUPS:
        Default udev rules use the following standard system group
        names, which need to be resolvable by getgrnam() at any time,
        even in the very early boot stages, where no other databases
        and network are available:

        audio, cdrom, dialout, disk, input, kmem, lp, tape, tty, video

        During runtime, the journal daemon requires the
        "systemd-journal" system group to exist. New journal files will
        be readable by this group (but not writable), which may be used
        to grant specific users read access. In addition, system
        groups "wheel" and "adm" will be given read-only access to
        journal files using systemd-tmpfiles.service.

        The journal gateway daemon requires the
        "systemd-journal-gateway" system user and group to
        exist. During execution this network facing service will drop
        privileges and assume this uid/gid for security reasons.

        Similarly, the NTP daemon requires the "systemd-timesync" system
        user and group to exist.

        Similarly, the network management daemon requires the
        "systemd-network" system user and group to exist.

        Similarly, the name resolution daemon requires the
        "systemd-resolve" system user and group to exist.

        Similarly, the coredump support requires the
        "systemd-coredump" system user and group to exist.

NSS:
        systemd ships with four glibc NSS modules:

        nss-myhostname resolves the local hostname to locally
        configured IP addresses, as well as "localhost" to
        127.0.0.1/::1.

        nss-resolve enables DNS resolution via the systemd-resolved
        DNS/LLMNR caching stub resolver "systemd-resolved".

        nss-mymachines enables resolution of all local containers registered
        with machined to their respective IP addresses. It also maps UID/GIDs
        ranges used by containers to useful names.

        nss-systemd enables resolution of all dynamically allocated service
        users. (See the DynamicUser= setting in unit files.)

        To make use of these NSS modules, please add them to the "hosts:",
        "passwd:" and "group:" lines in /etc/nsswitch.conf. The "resolve"
        module should replace the glibc "dns" module in this file (and don't
        worry, it chain-loads the "dns" module if it can't talk to resolved).

        The four modules should be used in the following order:

                passwd: compat mymachines systemd
                group: compat mymachines systemd
                hosts: files mymachines resolve myhostname

SYSV INIT.D SCRIPTS:
        When calling "systemctl enable/disable/is-enabled" on a unit which is a
        SysV init.d script, it calls /usr/lib/systemd/systemd-sysv-install;
        this needs to translate the action into the distribution specific
        mechanism such as chkconfig or update-rc.d. Packagers need to provide
        this script if you need this functionality (you don't if you disabled
        SysV init support).

        Please see src/systemctl/systemd-sysv-install.SKELETON for how this
        needs to look like, and provide an implementation at the marked places.

WARNINGS:
        systemd will warn you during boot if /usr is on a different
        file system than /. While in systemd itself very little will
        break if /usr is on a separate partition, many of its
        dependencies very likely will break sooner or later in one
        form or another. For example, udev rules tend to refer to
        binaries in /usr, binaries that link to libraries in /usr or
        binaries that refer to data files in /usr. Since these
        breakages are not always directly visible, systemd will warn
        about this, since this kind of file system setup is not really
        supported anymore by the basic set of Linux OS components.

        systemd requires that the /run mount point exists. systemd also
        requires that /var/run is a symlink to /run.

        For more information on this issue consult
        https://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken

        To run systemd under valgrind, compile with VALGRIND defined
        (e.g. ./configure CPPFLAGS='... -DVALGRIND=1'). Otherwise,
        false positives will be triggered by code which violates
        some rules but is actually safe.

ENGINEERING AND CONSULTING SERVICES:
        Kinvolk (https://kinvolk.io) offers professional engineering
        and consulting services for systemd. Please contact Chris Kühl
        <chris@kinvolk.io> for more information.