54c8732c46
Enable the PRV_Name2IPAddress() function with seccomp support and start the helper process before loading the seccomp filter (but after dropping root privileges). This will move the getaddrinfo() call outside the seccomp filter and should make it more reliable as the list of required system calls won't depend on what glibc NSS modules are used on the system.
166 lines
6.5 KiB
Groff
166 lines
6.5 KiB
Groff
.TH CHRONYD 8 "@MAN_DATE@" "chrony @VERSION@" "System Administration"
|
|
.SH NAME
|
|
chronyd \- chrony background daemon
|
|
|
|
.SH SYNOPSIS
|
|
.B chronyd
|
|
[\fIOPTIONS\fR] [\fIconfiguration commands\fR]
|
|
|
|
.SH DESCRIPTION
|
|
\fIchrony\fR is a pair of programs for maintaining the accuracy of computer
|
|
clocks. \fBchronyd\fR is a background daemon program that can be started at boot
|
|
time.
|
|
|
|
\fBchronyd\fR is a daemon which runs in background on the
|
|
system. It obtains measurements (e.g. via the network) of the
|
|
system's offset relative to other systems, and adjusts the system
|
|
time accordingly. For isolated systems, the user can periodically
|
|
enter the correct time by hand (using \fIchronyc\fR). In either case,
|
|
\fBchronyd\fR determines the rate at which the computer
|
|
gains or loses time, and compensates for this.
|
|
|
|
.SH USAGE
|
|
\fBchronyd\fR is usually started at boot-time and requires superuser
|
|
privileges.
|
|
|
|
If \fBchronyd\fR has been installed to its default location
|
|
\fI@SBINDIR@/chronyd\fR, starting it is simply a matter of entering the
|
|
command:
|
|
|
|
\fI@SBINDIR@/chronyd\fR
|
|
|
|
Information messages and warnings will be logged to syslog.
|
|
|
|
If no configuration commands are specified on the command line,
|
|
\fBchronyd\fR will read the commands from the configuration file
|
|
(default \fI@SYSCONFDIR@/chrony.conf\fR).
|
|
|
|
.SH OPTIONS
|
|
A summary of the options supported by \fBchronyd\fR is included below.
|
|
|
|
.TP
|
|
\fB\-P\fR \fIpriority\fR
|
|
On Linux, this option will select the SCHED_FIFO real-time scheduler at the
|
|
specified priority (which must be between 0 and 100). On Mac OS X, this
|
|
option must have either a value of 0 (the default) to disable the thread
|
|
time constraint policy or 1 for the policy to be enabled. Other systems do not
|
|
support this option.
|
|
.TP
|
|
.B \-m
|
|
This option will lock chronyd into RAM so that it will never be paged out.
|
|
This mode is only supported on Linux.
|
|
.TP
|
|
.B \-n
|
|
When run in this mode, the program will not detach itself from the
|
|
terminal.
|
|
.TP
|
|
.B \-d
|
|
When run in this mode, the program will not detach itself from the
|
|
terminal, and all messages will be sent to the terminal instead of
|
|
to syslog. When \fBchronyd\fR was compiled with debugging support,
|
|
this option can be used twice to print also debugging messages.
|
|
.TP
|
|
\fB\-f\fR \fIconf-file\fR
|
|
This option can be used to specify an alternate location for the
|
|
configuration file (default \fI@SYSCONFDIR@/chrony.conf\fR).
|
|
.TP
|
|
.B \-r
|
|
This option will reload sample histories for each of the servers being used.
|
|
These histories are created by using the \fIdump\fR command in \fIchronyc\fR,
|
|
or by setting the \fIdumponexit\fR directive in the configuration file. This
|
|
option is useful if you want to stop and restart \fBchronyd\fR briefly for any
|
|
reason, e.g. to install a new version. However, it should be used only on
|
|
systems where the kernel can maintain clock compensation whilst not under
|
|
\fBchronyd\fR's control (i.e. Linux, FreeBSD, NetBSD and Solaris).
|
|
.TP
|
|
.B \-R
|
|
When this option is used, the \fIinitstepslew\fR directive and the
|
|
\fImakestep\fR directive used with a positive limit will be ignored. This
|
|
option is useful when restarting \fBchronyd\fR and can be used in conjunction
|
|
with the \fB-r\fR option.
|
|
.TP
|
|
.B \-s
|
|
This option will set the system clock from the computer's real-time clock or
|
|
to the last modification time of the file specified by the \fIdriftfile\fR
|
|
directive. Real-time clocks are supported only on Linux.
|
|
|
|
If used in conjunction with the \fB-r\fR flag, \fBchronyd\fR will attempt
|
|
to preserve the old samples after setting the system clock from
|
|
the real time clock (RTC). This can be used to allow \fBchronyd\fR to
|
|
perform long term averaging of the gain or loss rate across system
|
|
reboots, and is useful for dial-up systems that are shut down when
|
|
not in use. For this to work well, it relies on \fBchronyd\fR having
|
|
been able to determine accurate statistics for the difference
|
|
between the RTC and system clock last time the computer was on.
|
|
|
|
If the last modification time of the drift file is later than the current time
|
|
and the RTC time, the system time will be set to it to restore the time when
|
|
\fBchronyd\fR was previously stopped. This is useful on computers that have no
|
|
RTC or the RTC is broken (e.g. it has no battery).
|
|
.TP
|
|
\fB\-u\fR \fIuser\fR
|
|
This option sets the name of the system user to which \fBchronyd\fR will switch
|
|
after start in order to drop root privileges. It overrides the \fBuser\fR
|
|
directive from the configuration file (default \fB@DEFAULT_USER@\fR).
|
|
|
|
On Linux, \fBchronyd\fR needs to be compiled with support for the \fBlibcap\fR
|
|
library. On Mac OS X, FreeBSD, NetBSD and Solaris \fBchronyd\fR forks into two
|
|
processes. The child process retains root privileges, but can only perform a
|
|
very limited range of privileged system calls on behalf of the parent.
|
|
.TP
|
|
\fB\-F\fR \fIlevel\fR
|
|
This option configures a system call filter when \fBchronyd\fR is compiled with
|
|
support for the Linux secure computing (seccomp) facility. In level 1 the
|
|
process is killed when a forbidden system call is made, in level -1 the SYSSIG
|
|
signal is thrown instead and in level 0 the filter is disabled (default 0).
|
|
|
|
It's recommended to enable the filter only when it's known to work on the
|
|
version of the system where \fBchrony\fR is installed as the filter needs to
|
|
allow also system calls made from libraries that \fBchronyd\fR is using (e.g.
|
|
libc) and different versions or implementations of the libraries may make
|
|
different system calls. If the filter is missing some system call,
|
|
\fBchronyd\fR could be killed even in normal operation.
|
|
.TP
|
|
.B \-q
|
|
When run in this mode, chronyd will set the system clock once
|
|
and exit. It will not detach from the terminal.
|
|
.TP
|
|
.B \-Q
|
|
This option is similar to \fB\-q\fR, but it will only print the offset and
|
|
not correct the clock.
|
|
.TP
|
|
.B \-v
|
|
This option displays \fBchronyd\fR's version number to the terminal and exits
|
|
.TP
|
|
.B \-4
|
|
Resolve hostnames only to IPv4 addresses and create only IPv4 sockets.
|
|
.TP
|
|
.B \-6
|
|
Resolve hostnames only to IPv6 addresses and create only IPv6 sockets.
|
|
|
|
.SH FILES
|
|
\fI@SYSCONFDIR@/chrony.conf\fR
|
|
|
|
.SH BUGS
|
|
To report bugs, please visit \fIhttp://chrony.tuxfamily.org/\fR
|
|
|
|
.SH "SEE ALSO"
|
|
\fBchronyd\fR is documented in detail in the documentation supplied with the
|
|
distribution (\fIchrony.txt\fR and \fIchrony.texi\fR).
|
|
|
|
.BR chronyc(1),
|
|
.BR chrony.conf(5),
|
|
.BR hwclock(8),
|
|
.BR ntpd(8)
|
|
|
|
.I http://chrony.tuxfamily.org/
|
|
|
|
.SH AUTHOR
|
|
Richard Curnow <rc@rc0.org.uk>
|
|
|
|
This man-page was written by Jan Schaumann <jschauma@netmeister.org> as part
|
|
of "The Missing Man Pages Project". Please see
|
|
\fIhttp://www.netmeister.org/misc/m2p2/index.html\fR for details.
|
|
|
|
The complete chrony documentation is supplied in texinfo format.
|
|
|