guix.texi

of a node under @file{/dev}, but its meaning depends on the @code{title}
field described below.

@item @code{title} (default: @code{'device})
This is a symbol that specifies how the @code{device} field is to be
interpreted.

When it is the symbol @code{device}, then the @code{device} field is
interpreted as a file name; when it is @code{label}, then @code{device}
is interpreted as a partition label name; when it is @code{uuid},
@code{device} is interpreted as a partition unique identifier (UUID).

UUIDs may be converted from their string representation (as shown by the
@command{tune2fs -l} command) using the @code{uuid} form@footnote{The
@code{uuid} form expects 16-byte UUIDs as defined in
@uref{https://tools.ietf.org/html/rfc4122, RFC@tie{}4122}.  This is the
form of UUID used by the ext2 family of file systems and others, but it
is different from ``UUIDs'' found in FAT file systems, for instance.},
like this:

@example
(file-system
  (mount-point "/home")
  (type "ext4")
  (title 'uuid)
  (device (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")))
@end example

The @code{label} and @code{uuid} options offer a way to refer to disk
partitions without having to hard-code their actual device
name@footnote{Note that, while it is tempting to use
@file{/dev/disk/by-uuid} and similar device names to achieve the same
result, this is not recommended: These special device nodes are created
by the udev daemon and may be unavailable at the time the device is
mounted.}.

However, when the source of a file system is a mapped device (@pxref{Mapped
Devices}), its @code{device} field @emph{must} refer to the mapped
device name---e.g., @file{/dev/mapper/root-partition}---and consequently
@code{title} must be set to @code{'device}.  This is required so that
the system knows that mounting the file system depends on having the
corresponding device mapping established.

@item @code{flags} (default: @code{'()})
This is a list of symbols denoting mount flags.  Recognized flags
include @code{read-only}, @code{bind-mount}, @code{no-dev} (disallow
access to special files), @code{no-suid} (ignore setuid and setgid
bits), and @code{no-exec} (disallow program execution.)

@item @code{options} (default: @code{#f})
This is either @code{#f}, or a string denoting mount options.

@item @code{mount?} (default: @code{#t})
This value indicates whether to automatically mount the file system when
the system is brought up.  When set to @code{#f}, the file system gets
an entry in @file{/etc/fstab} (read by the @command{mount} command) but
is not automatically mounted.

@item @code{needed-for-boot?} (default: @code{#f})
This Boolean value indicates whether the file system is needed when
booting.  If that is true, then the file system is mounted when the
initial RAM disk (initrd) is loaded.  This is always the case, for
instance, for the root file system.

@item @code{check?} (default: @code{#t})
This Boolean indicates whether the file system needs to be checked for
errors before being mounted.

@item @code{create-mount-point?} (default: @code{#f})
When true, the mount point is created if it does not exist yet.

@item @code{dependencies} (default: @code{'()})
This is a list of @code{<file-system>} or @code{<mapped-device>} objects
representing file systems that must be mounted or mapped devices that
must be opened before (and unmounted or closed after) this one.

As an example, consider a hierarchy of mounts: @file{/sys/fs/cgroup} is
a dependency of @file{/sys/fs/cgroup/cpu} and
@file{/sys/fs/cgroup/memory}.

Another example is a file system that depends on a mapped device, for
example for an encrypted partition (@pxref{Mapped Devices}).
@end table
@end deftp

The @code{(gnu system file-systems)} exports the following useful
variables.

@defvr {Scheme Variable} %base-file-systems
These are essential file systems that are required on normal systems,
such as @var{%pseudo-terminal-file-system} and @var{%immutable-store} (see
below.)  Operating system declarations should always contain at least
these.
@end defvr

@defvr {Scheme Variable} %pseudo-terminal-file-system
This is the file system to be mounted as @file{/dev/pts}.  It supports
@dfn{pseudo-terminals} created @i{via} @code{openpty} and similar
functions (@pxref{Pseudo-Terminals,,, libc, The GNU C Library Reference
Manual}).  Pseudo-terminals are used by terminal emulators such as
@command{xterm}.
@end defvr

@defvr {Scheme Variable} %shared-memory-file-system
This file system is mounted as @file{/dev/shm} and is used to support
memory sharing across processes (@pxref{Memory-mapped I/O,
@code{shm_open},, libc, The GNU C Library Reference Manual}).
@end defvr

@defvr {Scheme Variable} %immutable-store
This file system performs a read-only ``bind mount'' of
@file{/gnu/store}, making it read-only for all the users including
@code{root}.  This prevents against accidental modification by software
running as @code{root} or by system administrators.

The daemon itself is still able to write to the store: it remounts it
read-write in its own ``name space.''
@end defvr

@defvr {Scheme Variable} %binary-format-file-system
The @code{binfmt_misc} file system, which allows handling of arbitrary
executable file types to be delegated to user space.  This requires the
@code{binfmt.ko} kernel module to be loaded.
@end defvr

@defvr {Scheme Variable} %fuse-control-file-system
The @code{fusectl} file system, which allows unprivileged users to mount
and unmount user-space FUSE file systems.  This requires the
@code{fuse.ko} kernel module to be loaded.
@end defvr

@node Mapped Devices
@subsection Mapped Devices

@cindex device mapping
@cindex mapped devices
The Linux kernel has a notion of @dfn{device mapping}: a block device,
such as a hard disk partition, can be @dfn{mapped} into another device,
usually in @code{/dev/mapper/},
with additional processing over the data that flows through
it@footnote{Note that the GNU@tie{}Hurd makes no difference between the
concept of a ``mapped device'' and that of a file system: both boil down
to @emph{translating} input/output operations made on a file to
operations on its backing store.  Thus, the Hurd implements mapped
devices, like file systems, using the generic @dfn{translator} mechanism
(@pxref{Translators,,, hurd, The GNU Hurd Reference Manual}).}.  A
typical example is encryption device mapping: all writes to the mapped
device are encrypted, and all reads are deciphered, transparently.
Guix extends this notion by considering any device or set of devices that
are @dfn{transformed} in some way to create a new device; for instance,
RAID devices are obtained by @dfn{assembling} several other devices, such
as hard disks or partitions, into a new one that behaves as one partition.
Other examples, not yet implemented, are LVM logical volumes.

Mapped devices are declared using the @code{mapped-device} form,
defined as follows; for examples, see below.

@deftp {Data Type} mapped-device
Objects of this type represent device mappings that will be made when
the system boots up.

@table @code
@item source
This is either a string specifying the name of the block device to be mapped,
such as @code{"/dev/sda3"}, or a list of such strings when several devices
need to be assembled for creating a new one.

@item target
This string specifies the name of the resulting mapped device.  For
kernel mappers such as encrypted devices of type @code{luks-device-mapping},
specifying @code{"my-partition"} leads to the creation of
the @code{"/dev/mapper/my-partition"} device.
For RAID devices of type @code{raid-device-mapping}, the full device name
such as @code{"/dev/md0"} needs to be given.

@item type
This must be a @code{mapped-device-kind} object, which specifies how
@var{source} is mapped to @var{target}.
@end table
@end deftp

@defvr {Scheme Variable} luks-device-mapping
This defines LUKS block device encryption using the @command{cryptsetup}
command from the package with the same name.  It relies on the
@code{dm-crypt} Linux kernel module.
@end defvr

@defvr {Scheme Variable} raid-device-mapping
This defines a RAID device, which is assembled using the @code{mdadm}
command from the package with the same name.  It requires a Linux kernel
module for the appropriate RAID level to be loaded, such as @code{raid456}
for RAID-4, RAID-5 or RAID-6, or @code{raid10} for RAID-10.
@end defvr

@cindex disk encryption
@cindex LUKS
The following example specifies a mapping from @file{/dev/sda3} to
@file{/dev/mapper/home} using LUKS---the
@url{https://gitlab.com/cryptsetup/cryptsetup,Linux Unified Key Setup}, a
standard mechanism for disk encryption.
The @file{/dev/mapper/home}
device can then be used as the @code{device} of a @code{file-system}
declaration (@pxref{File Systems}).

@example
(mapped-device
  (source "/dev/sda3")
  (target "home")
  (type luks-device-mapping))
@end example

Alternatively, to become independent of device numbering, one may obtain
the LUKS UUID (@dfn{unique identifier}) of the source device by a
command like:

@example
cryptsetup luksUUID /dev/sda3
@end example

and use it as follows:

@example
(mapped-device
  (source (uuid "cb67fc72-0d54-4c88-9d4b-b225f30b0f44"))
  (target "home")
  (type luks-device-mapping))
@end example

@cindex swap encryption
It is also desirable to encrypt swap space, since swap space may contain
sensitive data.  One way to accomplish that is to use a swap file in a
file system on a device mapped via LUKS encryption.  In this way, the
swap file is encrypted because the entire device is encrypted.
@xref{Preparing for Installation,,Disk Partitioning}, for an example.

A RAID device formed of the partitions @file{/dev/sda1} and @file{/dev/sdb1}
may be declared as follows:

@example
(mapped-device
  (source (list "/dev/sda1" "/dev/sdb1"))
  (target "/dev/md0")
  (type raid-device-mapping))
@end example

The @file{/dev/md0} device can then be used as the @code{device} of a
@code{file-system} declaration (@pxref{File Systems}).
Note that the RAID level need not be given; it is chosen during the
initial creation and formatting of the RAID device and is determined
automatically later.


@node User Accounts
@subsection User Accounts

@cindex users
@cindex accounts
@cindex user accounts
User accounts and groups are entirely managed through the
@code{operating-system} declaration.  They are specified with the
@code{user-account} and @code{user-group} forms:

@example
(user-account
  (name "alice")
  (group "users")
  (supplementary-groups '("wheel"   ;allow use of sudo, etc.
                          "audio"   ;sound card
                          "video"   ;video devices such as webcams
                          "cdrom")) ;the good ol' CD-ROM
  (comment "Bob's sister")
  (home-directory "/home/alice"))
@end example

When booting or upon completion of @command{guix system reconfigure},
the system ensures that only the user accounts and groups specified in
the @code{operating-system} declaration exist, and with the specified
properties.  Thus, account or group creations or modifications made by
directly invoking commands such as @command{useradd} are lost upon
reconfiguration or reboot.  This ensures that the system remains exactly
as declared.

@deftp {Data Type} user-account
Objects of this type represent user accounts.  The following members may
be specified:

@table @asis
@item @code{name}
The name of the user account.

@item @code{group}
@cindex groups
This is the name (a string) or identifier (a number) of the user group
this account belongs to.

@item @code{supplementary-groups} (default: @code{'()})
Optionally, this can be defined as a list of group names that this
account belongs to.

@item @code{uid} (default: @code{#f})
This is the user ID for this account (a number), or @code{#f}.  In the
latter case, a number is automatically chosen by the system when the
account is created.

@item @code{comment} (default: @code{""})
A comment about the account, such as the account owner's full name.

@item @code{home-directory}
This is the name of the home directory for the account.

@item @code{create-home-directory?} (default: @code{#t})
Indicates whether the home directory of this account should be created
if it does not exist yet.

@item @code{shell} (default: Bash)
This is a G-expression denoting the file name of a program to be used as
the shell (@pxref{G-Expressions}).

@item @code{system?} (default: @code{#f})
This Boolean value indicates whether the account is a ``system''
account.  System accounts are sometimes treated specially; for instance,
graphical login managers do not list them.

@anchor{user-account-password}
@item @code{password} (default: @code{#f})
You would normally leave this field to @code{#f}, initialize user
passwords as @code{root} with the @command{passwd} command, and then let
users change it with @command{passwd}.  Passwords set with
@command{passwd} are of course preserved across reboot and
reconfiguration.

If you @emph{do} want to have a preset password for an account, then
this field must contain the encrypted password, as a string.
@xref{crypt,,, libc, The GNU C Library Reference Manual}, for more information
on password encryption, and @ref{Encryption,,, guile, GNU Guile Reference
Manual}, for information on Guile's @code{crypt} procedure.

@end table
@end deftp

@cindex groups
User group declarations are even simpler:

@example
(user-group (name "students"))
@end example

@deftp {Data Type} user-group
This type is for, well, user groups.  There are just a few fields:

@table @asis
@item @code{name}
The name of the group.

@item @code{id} (default: @code{#f})
The group identifier (a number).  If @code{#f}, a new number is
automatically allocated when the group is created.

@item @code{system?} (default: @code{#f})
This Boolean value indicates whether the group is a ``system'' group.
System groups have low numerical IDs.

@item @code{password} (default: @code{#f})
What, user groups can have a password?  Well, apparently yes.  Unless
@code{#f}, this field specifies the password of the group.

@end table
@end deftp

For convenience, a variable lists all the basic user groups one may
expect:

@defvr {Scheme Variable} %base-groups
This is the list of basic user groups that users and/or packages expect
to be present on the system.  This includes groups such as ``root'',
``wheel'', and ``users'', as well as groups used to control access to
specific devices such as ``audio'', ``disk'', and ``cdrom''.
@end defvr

@defvr {Scheme Variable} %base-user-accounts
This is the list of basic system accounts that programs may expect to
find on a GNU/Linux system, such as the ``nobody'' account.

Note that the ``root'' account is not included here.  It is a
special-case and is automatically added whether or not it is specified.
@end defvr

@node Locales
@subsection Locales

@cindex locale
A @dfn{locale} defines cultural conventions for a particular language
and region of the world (@pxref{Locales,,, libc, The GNU C Library
Reference Manual}).  Each locale has a name that typically has the form
@code{@var{language}_@var{territory}.@var{codeset}}---e.g.,
@code{fr_LU.utf8} designates the locale for the French language, with
cultural conventions from Luxembourg, and using the UTF-8 encoding.

@cindex locale definition
Usually, you will want to specify the default locale for the machine
using the @code{locale} field of the @code{operating-system} declaration
(@pxref{operating-system Reference, @code{locale}}).

The selected locale is automatically added to the @dfn{locale
definitions} known to the system if needed, with its codeset inferred
from its name---e.g., @code{bo_CN.utf8} will be assumed to use the
@code{UTF-8} codeset.  Additional locale definitions can be specified in
the @code{locale-definitions} slot of @code{operating-system}---this is
useful, for instance, if the codeset could not be inferred from the
locale name.  The default set of locale definitions includes some widely
used locales, but not all the available locales, in order to save space.

For instance, to add the North Frisian locale for Germany, the value of
that field may be:

@example
(cons (locale-definition
        (name "fy_DE.utf8") (source "fy_DE"))
      %default-locale-definitions)
@end example

Likewise, to save space, one might want @code{locale-definitions} to
list only the locales that are actually used, as in:

@example
(list (locale-definition
        (name "ja_JP.eucjp") (source "ja_JP")
        (charset "EUC-JP")))
@end example

@vindex LOCPATH
The compiled locale definitions are available at
@file{/run/current-system/locale/X.Y}, where @code{X.Y} is the libc
version, which is the default location where the GNU@tie{}libc provided
by Guix looks for locale data.  This can be overridden using the
@code{LOCPATH} environment variable (@pxref{locales-and-locpath,
@code{LOCPATH} and locale packages}).

The @code{locale-definition} form is provided by the @code{(gnu system
locale)} module.  Details are given below.

@deftp {Data Type} locale-definition
This is the data type of a locale definition.

@table @asis

@item @code{name}
The name of the locale.  @xref{Locale Names,,, libc, The GNU C Library
Reference Manual}, for more information on locale names.

@item @code{source}
The name of the source for that locale.  This is typically the
@code{@var{language}_@var{territory}} part of the locale name.

@item @code{charset} (default: @code{"UTF-8"})
The ``character set'' or ``code set'' for that locale,
@uref{http://www.iana.org/assignments/character-sets, as defined by
IANA}.

@end table
@end deftp

@defvr {Scheme Variable} %default-locale-definitions
A list of commonly used UTF-8 locales, used as the default
value of the @code{locale-definitions} field of @code{operating-system}
declarations.

@cindex locale name
@cindex normalized codeset in locale names
These locale definitions use the @dfn{normalized codeset} for the part
that follows the dot in the name (@pxref{Using gettextized software,
normalized codeset,, libc, The GNU C Library Reference Manual}).  So for
instance it has @code{uk_UA.utf8} but @emph{not}, say,
@code{uk_UA.UTF-8}.
@end defvr

@subsubsection Locale Data Compatibility Considerations

@cindex incompatibility, of locale data
@code{operating-system} declarations provide a @code{locale-libcs} field
to specify the GNU@tie{}libc packages that are used to compile locale
declarations (@pxref{operating-system Reference}).  ``Why would I
care?'', you may ask.  Well, it turns out that the binary format of
locale data is occasionally incompatible from one libc version to
another.

@c See <https://sourceware.org/ml/libc-alpha/2015-09/msg00575.html>
@c and <https://lists.gnu.org/archive/html/guix-devel/2015-08/msg00737.html>.
For instance, a program linked against libc version 2.21 is unable to
read locale data produced with libc 2.22; worse, that program
@emph{aborts} instead of simply ignoring the incompatible locale
data@footnote{Versions 2.23 and later of GNU@tie{}libc will simply skip
the incompatible locale data, which is already an improvement.}.
Similarly, a program linked against libc 2.22 can read most, but not
all, of the locale data from libc 2.21 (specifically, @code{LC_COLLATE}
data is incompatible); thus calls to @code{setlocale} may fail, but
programs will not abort.

The ``problem'' in GuixSD is that users have a lot of freedom: They can
choose whether and when to upgrade software in their profiles, and might
be using a libc version different from the one the system administrator
used to build the system-wide locale data.

Fortunately, unprivileged users can also install their own locale data
and define @var{GUIX_LOCPATH} accordingly (@pxref{locales-and-locpath,
@code{GUIX_LOCPATH} and locale packages}).

Still, it is best if the system-wide locale data at
@file{/run/current-system/locale} is built for all the libc versions
actually in use on the system, so that all the programs can access
it---this is especially crucial on a multi-user system.  To do that, the
administrator can specify several libc packages in the
@code{locale-libcs} field of @code{operating-system}:

@example
(use-package-modules base)

(operating-system
  ;; @dots{}
  (locale-libcs (list glibc-2.21 (canonical-package glibc))))
@end example

This example would lead to a system containing locale definitions for
both libc 2.21 and the current version of libc in
@file{/run/current-system/locale}.


@node Services
@subsection Services

@cindex system services
An important part of preparing an @code{operating-system} declaration is
listing @dfn{system services} and their configuration (@pxref{Using the
Configuration System}).  System services are typically daemons launched
when the system boots, or other actions needed at that time---e.g.,
configuring network access.

GuixSD has a broad definition of ``service'' (@pxref{Service
Composition}), but many services are managed by the GNU@tie{}Shepherd
(@pxref{Shepherd Services}).  On a running system, the @command{herd}
command allows you to list the available services, show their status,
start and stop them, or do other specific operations (@pxref{Jump
Start,,, shepherd, The GNU Shepherd Manual}).  For example:

@example
# herd status
@end example

The above command, run as @code{root}, lists the currently defined
services.  The @command{herd doc} command shows a synopsis of the given
service:

@example
# herd doc nscd
Run libc's name service cache daemon (nscd).
@end example

The @command{start}, @command{stop}, and @command{restart} sub-commands
have the effect you would expect.  For instance, the commands below stop
the nscd service and restart the Xorg display server:

@example
# herd stop nscd
Service nscd has been stopped.
# herd restart xorg-server
Service xorg-server has been stopped.
Service xorg-server has been started.
@end example

The following sections document the available services, starting with
the core services, that may be used in an @code{operating-system}
declaration.

@menu
* Base Services::               Essential system services.
* Scheduled Job Execution::     The mcron service.
* Log Rotation::                The rottlog service.
* Networking Services::         Network setup, SSH daemon, etc.
* X Window::                    Graphical display.
* Printing Services::           Local and remote printer support.
* Desktop Services::            D-Bus and desktop services.
* Database Services::           SQL databases.
* Mail Services::               IMAP, POP3, SMTP, and all that.
* Messaging Services::          Messaging services.
* Kerberos Services::           Kerberos services.
* Web Services::                Web servers.
* VPN Services::                VPN daemons.
* Network File System::         NFS related services.
* Continuous Integration::      The Cuirass service.
* Power management Services::   The TLP tool.
* Miscellaneous Services::      Other services.
@end menu

@node Base Services
@subsubsection Base Services

The @code{(gnu services base)} module provides definitions for the basic
services that one expects from the system.  The services exported by
this module are listed below.

@defvr {Scheme Variable} %base-services
This variable contains a list of basic services (@pxref{Service Types
and Services}, for more information on service objects) one would
expect from the system: a login service (mingetty) on each tty, syslogd,
the libc name service cache daemon (nscd), the udev device manager, and
more.

This is the default value of the @code{services} field of
@code{operating-system} declarations.  Usually, when customizing a
system, you will want to append services to @var{%base-services}, like
this:

@example
(cons* (avahi-service) (lsh-service) %base-services)
@end example
@end defvr

@defvr {Scheme Variable} special-files-service-type
This is the service that sets up ``special files'' such as
@file{/bin/sh}; an instance of it is part of @code{%base-services}.

The value associated with @code{special-files-service-type} services
must be a list of tuples where the first element is the ``special file''
and the second element is its target.  By default it is:

@cindex @file{/bin/sh}
@cindex @file{sh}, in @file{/bin}
@example
`(("/bin/sh" ,(file-append @var{bash} "/bin/sh")))
@end example

@cindex @file{/usr/bin/env}
@cindex @file{env}, in @file{/usr/bin}
If you want to add, say, @code{/usr/bin/env} to your system, you can
change it to:

@example
`(("/bin/sh" ,(file-append @var{bash} "/bin/sh"))
  ("/usr/bin/env" ,(file-append @var{coreutils} "/bin/env")))
@end example

Since this is part of @code{%base-services}, you can use
@code{modify-services} to customize the set of special files
(@pxref{Service Reference, @code{modify-services}}).  But the simple way
to add a special file is @i{via} the @code{extra-special-file} procedure
(see below.)
@end defvr

@deffn {Scheme Procedure} extra-special-file @var{file} @var{target}
Use @var{target} as the ``special file'' @var{file}.

For example, adding the following lines to the @code{services} field of
your operating system declaration leads to a @file{/usr/bin/env}
symlink:

@example
(extra-special-file "/usr/bin/env"
                    (file-append coreutils "/bin/env"))
@end example
@end deffn

@deffn {Scheme Procedure} host-name-service @var{name}
Return a service that sets the host name to @var{name}.
@end deffn

@deffn {Scheme Procedure} login-service @var{config}
Return a service to run login according to @var{config}, a
@code{<login-configuration>} object, which specifies the message of the day,
among other things.
@end deffn

@deftp {Data Type} login-configuration
This is the data type representing the configuration of login.

@table @asis

@item @code{motd}
@cindex message of the day
A file-like object containing the ``message of the day''.

@item @code{allow-empty-passwords?} (default: @code{#t})
Allow empty passwords by default so that first-time users can log in when
the 'root' account has just been created.

@end table
@end deftp

@deffn {Scheme Procedure} mingetty-service @var{config}
Return a service to run mingetty according to @var{config}, a
@code{<mingetty-configuration>} object, which specifies the tty to run, among
other things.
@end deffn

@deftp {Data Type} mingetty-configuration
This is the data type representing the configuration of Mingetty, which
provides the default implementation of virtual console log-in.

@table @asis

@item @code{tty}
The name of the console this Mingetty runs on---e.g., @code{"tty1"}.

@item @code{auto-login} (default: @code{#f})
When true, this field must be a string denoting the user name under
which the system automatically logs in.  When it is @code{#f}, a
user name and password must be entered to log in.

@item @code{login-program} (default: @code{#f})
This must be either @code{#f}, in which case the default log-in program
is used (@command{login} from the Shadow tool suite), or a gexp denoting
the name of the log-in program.

@item @code{login-pause?} (default: @code{#f})
When set to @code{#t} in conjunction with @var{auto-login}, the user
will have to press a key before the log-in shell is launched.

@item @code{mingetty} (default: @var{mingetty})
The Mingetty package to use.

@end table
@end deftp

@deffn {Scheme Procedure} agetty-service @var{config}
Return a service to run agetty according to @var{config}, an
@code{<agetty-configuration>} object, which specifies the tty to run,
among other things.
@end deffn

@deftp {Data Type} agetty-configuration
This is the data type representing the configuration of agetty, which
implements virtual and serial console log-in.  See the @code{agetty(8)}
man page for more information.

@table @asis

@item @code{tty}
The name of the console this agetty runs on, as a string---e.g.,
@code{"ttyS0"}. This argument is mandatory.

@item @code{baud-rate} (default: @code{#f})
A string containing a comma-separated list of one or more baud rates, in
descending order.

@item @code{term} (default: @code{#f})
A string containing the value used for the @code{TERM} environment
variable.

@item @code{eight-bits?} (default: @code{#f})
When @code{#t}, the tty is assumed to be 8-bit clean, and parity detection is
disabled.

@item @code{auto-login} (default: @code{#f})
When passed a login name, as a string, the specified user will be logged
in automatically without prompting for their login name or password.

@item @code{no-reset?} (default: @code{#f})
When @code{#t}, don't reset terminal cflags (control modes).

@item @code{host} (default: @code{#f})
This accepts a string containing the "login_host", which will be written
into the @file{/var/run/utmpx} file.

@item @code{remote?} (default: @code{#f})
When set to @code{#t} in conjunction with @var{host}, this will add an
@code{-r} fakehost option to the command line of the login program
specified in @var{login-program}.

@item @code{flow-control?} (default: @code{#f})
When set to @code{#t}, enable hardware (RTS/CTS) flow control.

@item @code{no-issue?} (default: @code{#f})
When set to @code{#t}, the contents of the @file{/etc/issue} file will
not be displayed before presenting the login prompt.

@item @code{init-string} (default: @code{#f})
This accepts a string that will be sent to the tty or modem before
sending anything else.  It can be used to initialize a modem.

@item @code{no-clear?} (default: @code{#f})
When set to @code{#t}, agetty will not clear the screen before showing
the login prompt.

@item @code{login-program} (default: (file-append shadow "/bin/login"))
This must be either a gexp denoting the name of a log-in program, or
unset, in which case the default value is the @command{login} from the
Shadow tool suite.

@item @code{local-line} (default: @code{#f})
Control the CLOCAL line flag.  This accepts one of three symbols as
arguments, @code{'auto}, @code{'always}, or @code{'never}. If @code{#f},
the default value chosen by agetty is @code{'auto}.

@item @code{extract-baud?} (default: @code{#f})
When set to @code{#t}, instruct agetty to try to extract the baud rate
from the status messages produced by certain types of modems.

@item @code{skip-login?} (default: @code{#f})
When set to @code{#t}, do not prompt the user for a login name.  This
can be used with @var{login-program} field to use non-standard login
systems.

@item @code{no-newline?} (default: @code{#f})
When set to @code{#t}, do not print a newline before printing the
@file{/etc/issue} file.

@c Is this dangerous only when used with login-program, or always?
@item @code{login-options} (default: @code{#f})
This option accepts a string containing options that are passed to the
login program.  When used with the @var{login-program}, be aware that a
malicious user could try to enter a login name containing embedded
options that could be parsed by the login program.

@item @code{login-pause} (default: @code{#f})
When set to @code{#t}, wait for any key before showing the login prompt.
This can be used in conjunction with @var{auto-login} to save memory by
lazily spawning shells.

@item @code{chroot} (default: @code{#f})
Change root to the specified directory.  This option accepts a directory
path as a string.

@item @code{hangup?} (default: @code{#f})
Use the Linux system call @code{vhangup} to do a virtual hangup of the
specified terminal.

@item @code{keep-baud?} (default: @code{#f})
When set to @code{#t}, try to keep the existing baud rate.  The baud
rates from @var{baud-rate} are used when agetty receives a @key{BREAK}
character.

@item @code{timeout} (default: @code{#f})
When set to an integer value, terminate if no user name could be read
within @var{timeout} seconds.

@item @code{detect-case?} (default: @code{#f})
When set to @code{#t}, turn on support for detecting an uppercase-only
terminal.  This setting will detect a login name containing only
uppercase letters as indicating an uppercase-only terminal and turn on
some upper-to-lower case conversions.  Note that this will not support
Unicode characters.

@item @code{wait-cr?} (default: @code{#f})
When set to @code{#t}, wait for the user or modem to send a
carriage-return or linefeed character before displaying
@file{/etc/issue} or login prompt.  This is typically used with the
@var{init-string} option.

@item @code{no-hints?} (default: @code{#f})
When set to @code{#t}, do not print hints about Num, Caps, and Scroll
locks.

@item @code{no-hostname?} (default: @code{#f})
By default, the hostname is printed.  When this option is set to
@code{#t}, no hostname will be shown at all.

@item @code{long-hostname?} (default: @code{#f})
By default, the hostname is only printed until the first dot.  When this
option is set to @code{#t}, the fully qualified hostname by
@code{gethostname} or @code{getaddrinfo} is shown.

@item @code{erase-characters} (default: @code{#f})
This option accepts a string of additional characters that should be
interpreted as backspace when the user types their login name.

@item @code{kill-characters} (default: @code{#f})
This option accepts a string that should be interpreted to mean "ignore
all previous characters" (also called a "kill" character) when the types
their login name.

@item @code{chdir} (default: @code{#f})
This option accepts, as a string, a directory path that will be changed
to before login.

@item @code{delay} (default: @code{#f})
This options accepts, as an integer, the number of seconds to sleep
before opening the tty and displaying the login prompt.

@item @code{nice} (default: @code{#f})
This option accepts, as an integer, the nice value with which to run the
@command{login} program.

@item @code{extra-options} (default: @code{'()})
This option provides an "escape hatch" for the user to provide arbitrary
command-line arguments to @command{agetty} as a list of strings.

@end table
@end deftp

@deffn {Scheme Procedure} kmscon-service-type @var{config}
Return a service to run @uref{https://www.freedesktop.org/wiki/Software/kmscon,kmscon}
according to @var{config}, a @code{<kmscon-configuration>} object, which
specifies the tty to run, among other things.
@end deffn

@deftp {Data Type} kmscon-configuration
This is the data type representing the configuration of Kmscon, which
implements virtual console log-in.

@table @asis

@item @code{virtual-terminal}
The name of the console this Kmscon runs on---e.g., @code{"tty1"}.

@item @code{login-program} (default: @code{#~(string-append #$shadow "/bin/login")})
A gexp denoting the name of the log-in program. The default log-in program is
@command{login} from the Shadow tool suite.

@item @code{login-arguments} (default: @code{'("-p")})
A list of arguments to pass to @command{login}.

@item @code{hardware-acceleration?} (default: #f)
Whether to use hardware acceleration.

@item @code{kmscon} (default: @var{kmscon})
The Kmscon package to use.

@end table
@end deftp

@cindex name service cache daemon
@cindex nscd
@deffn {Scheme Procedure} nscd-service [@var{config}] [#:glibc glibc] @
                [#:name-services '()]
Return a service that runs the libc name service cache daemon (nscd) with the
given @var{config}---an @code{<nscd-configuration>} object.  @xref{Name
Service Switch}, for an example.
@end deffn

@defvr {Scheme Variable} %nscd-default-configuration
This is the default @code{<nscd-configuration>} value (see below) used
by @code{nscd-service}.  It uses the caches defined by
@var{%nscd-default-caches}; see below.
@end defvr

@deftp {Data Type} nscd-configuration
This is the data type representing the name service cache daemon (nscd)
configuration.

@table @asis

@item @code{name-services} (default: @code{'()})
List of packages denoting @dfn{name services} that must be visible to
the nscd---e.g., @code{(list @var{nss-mdns})}.

@item @code{glibc} (default: @var{glibc})
Package object denoting the GNU C Library providing the @command{nscd}
command.

@item @code{log-file} (default: @code{"/var/log/nscd.log"})
Name of the nscd log file.  This is where debugging output goes when
@code{debug-level} is strictly positive.

@item @code{debug-level} (default: @code{0})
Integer denoting the debugging levels.  Higher numbers mean that more
debugging output is logged.

@item @code{caches} (default: @var{%nscd-default-caches})
List of @code{<nscd-cache>} objects denoting things to be cached; see
below.

@end table
@end deftp

@deftp {Data Type} nscd-cache
Data type representing a cache database of nscd and its parameters.

@table @asis

@item @code{database}
This is a symbol representing the name of the database to be cached.
Valid values are @code{passwd}, @code{group}, @code{hosts}, and
@code{services}, which designate the corresponding NSS database
(@pxref{NSS Basics,,, libc, The GNU C Library Reference Manual}).

@item @code{positive-time-to-live}
@itemx @code{negative-time-to-live} (default: @code{20})
A number representing the number of seconds during which a positive or
negative lookup result remains in cache.

@item @code{check-files?} (default: @code{#t})
Whether to check for updates of the files corresponding to
@var{database}.

For instance, when @var{database} is @code{hosts}, setting this flag
instructs nscd to check for updates in @file{/etc/hosts} and to take
them into account.

@item @code{persistent?} (default: @code{#t})
Whether the cache should be stored persistently on disk.

@item @code{shared?} (default: @code{#t})
Whether the cache should be shared among users.

@item @code{max-database-size} (default: 32@tie{}MiB)
Maximum size in bytes of the database cache.

@c XXX: 'suggested-size' and 'auto-propagate?' seem to be expert
@c settings, so leave them out.

@end table