| '\" t |
| .\" Title: chronyd |
| .\" Author: [see the "AUTHOR(S)" section] |
| .\" Generator: Asciidoctor 2.0.15 |
| .\" Date: 2021-12-16 |
| .\" Manual: System Administration |
| .\" Source: chrony @CHRONY_VERSION@ |
| .\" Language: English |
| .\" |
| .TH "CHRONYD" "8" "2021-12-16" "chrony @CHRONY_VERSION@" "System Administration" |
| .ie \n(.g .ds Aq \(aq |
| .el .ds Aq ' |
| .ss \n[.ss] 0 |
| .nh |
| .ad l |
| .de URL |
| \fI\\$2\fP <\\$1>\\$3 |
| .. |
| .als MTO URL |
| .if \n[.g] \{\ |
| . mso www.tmac |
| . am URL |
| . ad l |
| . . |
| . am MTO |
| . ad l |
| . . |
| . LINKSTYLE blue R < > |
| .\} |
| .SH "NAME" |
| chronyd \- chrony daemon |
| .SH "SYNOPSIS" |
| .sp |
| \fBchronyd\fP [\fIOPTION\fP]... [\fIDIRECTIVE\fP]... |
| .SH "DESCRIPTION" |
| .sp |
| \fBchronyd\fP is a daemon for synchronisation of the system clock. It can |
| synchronise the clock with NTP servers, reference clocks (e.g. a GPS receiver), |
| and manual input using wristwatch and keyboard via \fBchronyc\fP. It can also |
| operate as an NTPv4 (RFC 5905) server and peer to provide a time service to |
| other computers in the network. |
| .sp |
| If no configuration directives are specified on the command line, \fBchronyd\fP |
| will read them from a configuration file. The compiled\-in default location of |
| the file is \fI@SYSCONFDIR@/chrony.conf\fP. |
| .sp |
| Informational messages, warnings, and errors will be logged to syslog. |
| .SH "OPTIONS" |
| .sp |
| \fB\-4\fP |
| .RS 4 |
| With this option hostnames will be resolved only to IPv4 addresses and only |
| IPv4 sockets will be created. |
| .RE |
| .sp |
| \fB\-6\fP |
| .RS 4 |
| With this option hostnames will be resolved only to IPv6 addresses and only |
| IPv6 sockets will be created. |
| .RE |
| .sp |
| \fB\-f\fP \fIfile\fP |
| .RS 4 |
| This option can be used to specify an alternate location for the configuration |
| file. The compiled\-in default value is \fI@SYSCONFDIR@/chrony.conf\fP. |
| .RE |
| .sp |
| \fB\-n\fP |
| .RS 4 |
| When run in this mode, the program will not detach itself from the terminal. |
| .RE |
| .sp |
| \fB\-d\fP |
| .RS 4 |
| When run in this mode, the program will not detach itself from the terminal, |
| and all messages will be written to the terminal instead of syslog. If |
| \fBchronyd\fP was compiled with enabled support for debugging, this option can be |
| used twice to enable debug messages. |
| .RE |
| .sp |
| \fB\-l\fP \fIfile\fP |
| .RS 4 |
| This option enables writing of log messages to a file instead of syslog or the |
| terminal. |
| .RE |
| .sp |
| \fB\-L\fP \fIlevel\fP |
| .RS 4 |
| This option specifies the minimum severity level of messages to be written to |
| the log file, syslog, or terminal. The following levels can be specified: |
| 0 (informational), 1 (warning), 2 (non\-fatal error), and 3 (fatal error). The |
| default value is 0. |
| .RE |
| .sp |
| \fB\-p\fP |
| .RS 4 |
| When run in this mode, \fBchronyd\fP will print the configuration and exit. It will |
| not detach from the terminal. This option can be used to verify the syntax of |
| the configuration and get the whole configuration, even if it is split into |
| multiple files and read by the \fBinclude\fP or \fBconfdir\fP directive. |
| .RE |
| .sp |
| \fB\-q\fP |
| .RS 4 |
| When run in this mode, \fBchronyd\fP will set the system clock once and exit. It |
| will not detach from the terminal. |
| .RE |
| .sp |
| \fB\-Q\fP |
| .RS 4 |
| This option is similar to the \fB\-q\fP option, except it only prints the offset |
| without making any corrections of the clock and it allows \fBchronyd\fP to be |
| started without root privileges. |
| .RE |
| .sp |
| \fB\-r\fP |
| .RS 4 |
| This option will try to reload and then delete files containing sample |
| histories for each of the servers and reference clocks being used. The |
| files are expected to be in the directory specified by the |
| \fBdumpdir\fP |
| directive in the configuration file. This option is useful if you want to stop |
| and restart \fBchronyd\fP 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\fP\(aqs control (i.e. Linux, FreeBSD, NetBSD, |
| illumos, and macOS 10.13 or later). |
| .RE |
| .sp |
| \fB\-R\fP |
| .RS 4 |
| When this option is used, the \fBinitstepslew\fP |
| directive and the \fBmakestep\fP directive used with |
| a positive limit will be ignored. This option is useful when restarting |
| \fBchronyd\fP and can be used in conjunction with the \fB\-r\fP option. |
| .RE |
| .sp |
| \fB\-s\fP |
| .RS 4 |
| This option will set the system clock from the computer\(cqs real\-time clock (RTC) |
| or to the last modification time of the file specified by the |
| \fBdriftfile\fP directive. Real\-time clocks are |
| supported only on Linux. |
| .sp |
| If used in conjunction with the \fB\-r\fP flag, \fBchronyd\fP will attempt to preserve |
| the old samples after setting the system clock from the RTC. This can be used |
| to allow \fBchronyd\fP to perform long term averaging of the gain or loss rate |
| across system reboots, and is useful for systems with intermittent access to |
| network that are shut down when not in use. For this to work well, it relies |
| on \fBchronyd\fP having been able to determine accurate statistics for the |
| difference between the RTC and system clock last time the computer was on. |
| .sp |
| If the last modification time of the drift file is later than both the current |
| time and the RTC time, the system time will be set to it to restore the time |
| when \fBchronyd\fP was previously stopped. This is useful on computers that have no |
| RTC or the RTC is broken (e.g. it has no battery). |
| .RE |
| .sp |
| \fB\-t\fP \fItimeout\fP |
| .RS 4 |
| This option sets a timeout (in seconds) after which \fBchronyd\fP will exit. If the |
| clock is not synchronised, it will exit with a non\-zero status. This is useful |
| with the \fB\-q\fP or \fB\-Q\fP option to shorten the maximum time waiting for |
| measurements, or with the \fB\-r\fP option to limit the time when \fBchronyd\fP is |
| running, but still allow it to adjust the frequency of the system clock. |
| .RE |
| .sp |
| \fB\-u\fP \fIuser\fP |
| .RS 4 |
| This option sets the name of the system user to which \fBchronyd\fP will switch |
| after start in order to drop root privileges. It overrides the |
| \fBuser\fP directive. The compiled\-in default value is |
| \fI@DEFAULT_USER@\fP. |
| .sp |
| On Linux, \fBchronyd\fP needs to be compiled with support for the \fBlibcap\fP library. |
| On macOS, FreeBSD, NetBSD, and illumos \fBchronyd\fP 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. |
| .RE |
| .sp |
| \fB\-U\fP |
| .RS 4 |
| This option disables a check for root privileges to allow \fBchronyd\fP to be |
| started under a non\-root user, assuming the process will have all capabilities |
| (e.g. provided by the service manager) and access to all files, directories, |
| and devices, needed to operate correctly in the specified configuration. Note |
| that different capabilities might be needed with different configurations and |
| different Linux kernel versions. Starting \fBchronyd\fP under a non\-root user is |
| not recommended when the configuration is not known, or at least limited to |
| specific directives. |
| .RE |
| .sp |
| \fB\-F\fP \fIlevel\fP |
| .RS 4 |
| This option configures system call filters loaded by \fBchronyd\fP processes if it |
| was compiled with support for the Linux secure computing (seccomp) facility. |
| Three levels are defined: 0, 1, 2. The filters are disabled at level 0. At |
| levels 1 and 2, \fBchronyd\fP will be killed if it makes a system call which is |
| blocked by the filters. The level can be specified as a negative number to |
| trigger the SIGSYS signal instead of SIGKILL, which can be useful for |
| debugging. The default value is 0. |
| .sp |
| At level 1, the filters allow only selected system calls that are normally |
| expected to be made by \fBchronyd\fP. Other system calls are blocked. This level is |
| recommended only if it is known to work on the version of the system where |
| \fBchrony\fP is installed. The filters need to allow also system calls made by |
| libraries that \fBchronyd\fP is using (e.g. libc), but different versions or |
| implementations of the libraries might make different system calls. If the |
| filters are missing a system call, \fBchronyd\fP could be killed even in normal |
| operation. |
| .sp |
| At level 2, the filters block only a small number of specific system calls |
| (e.g. fork and exec). This approach should avoid false positives, but the |
| protection of the system against a compromised \fBchronyd\fP process is much more |
| limited. |
| .sp |
| The filters cannot be enabled with the \fBmailonchange\fP directive. |
| .RE |
| .sp |
| \fB\-P\fP \fIpriority\fP |
| .RS 4 |
| On Linux, FreeBSD, NetBSD, and illumos this option will select the SCHED_FIFO |
| real\-time scheduler at the specified priority (which must be between 0 and |
| 100). On macOS, this option must have either a value of 0 to disable the thread |
| time constraint policy or 1 for the policy to be enabled. Other systems do not |
| support this option. The default value is 0. |
| .RE |
| .sp |
| \fB\-m\fP |
| .RS 4 |
| This option will lock \fBchronyd\fP into RAM so that it will never be paged out. |
| This mode is only supported on Linux, FreeBSD, NetBSD, and illumos. |
| .RE |
| .sp |
| \fB\-x\fP |
| .RS 4 |
| This option disables the control of the system clock. \fBchronyd\fP will not try to |
| make any adjustments of the clock. It will assume the clock is free running and |
| still track its offset and frequency relative to the estimated true time. This |
| option allows \fBchronyd\fP to be started without the capability to adjust or set |
| the system clock (e.g. in some containers) to operate as an NTP server. |
| .RE |
| .sp |
| \fB\-v\fP, \fB\-\-version\fP |
| .RS 4 |
| With this option \fBchronyd\fP will print version number to the terminal and exit. |
| .RE |
| .sp |
| \fB\-h\fP, \fB\-\-help\fP |
| .RS 4 |
| With this option \fBchronyd\fP will print a help message to the terminal and exit. |
| .RE |
| .SH "FILES" |
| .sp |
| \fI@SYSCONFDIR@/chrony.conf\fP |
| .SH "SEE ALSO" |
| .sp |
| \fBchronyc(1)\fP, \fBchrony.conf(5)\fP |
| .SH "BUGS" |
| .sp |
| For instructions on how to report bugs, please visit |
| .URL "https://chrony.tuxfamily.org/" "" "." |
| .SH "AUTHORS" |
| .sp |
| chrony was written by Richard Curnow, Miroslav Lichvar, and others. |