JAIL.CONF(5) FreeBSD File Formats Manual JAIL.CONF(5)
NAME
jail.conf - configuration file for system jails
DESCRIPTION
The jail.conf file consists of one or more jail definitions statements
for use by the jail(8) management program. A jail definition statement
consists of a single word, the name of the jail, an opening curly brace,
a list of at least two parameter assignments, and a closing curly brace.
A parameter assignment consists of a single word, the parameter name, an
equals sign, a value enclosed in double quotes, and a terminating
semicolon.
The syntax of a jail definition is as follows:
jailname {
parameter = "value";
...
}
This is used by jail(8) to specify a jail on the command line and report
the jail status, and is also passed to the kernel when creating the jail.
Parameters
A jail is defined by a set of named parameters, specified inside the jail
definition. See jail(8) for a list of jail parameters passed to the
kernel, as well as internal parameters used when creating and removing
jails.
A typical parameter has a name and a value. Some parameters are boolean
and may be specified with values of "true" or "false", or as valueless
shortcuts, with a "no" prefix indicating a false value. For example,
these are equivalent:
allow.mount = "false";
allow.nomount;
Other parameters may have more than one value. A comma-separated list of
values may be set in a single statement, or an existing parameter list
may be appended to using "+=":
ip4.addr = 10.1.1.1, 10.1.1.2, 10.1.1.3;
ip4.addr = 10.1.1.1;
ip4.addr += 10.1.1.2;
ip4.addr += 10.1.1.3;
Note the name parameter is implicitly set to the name in the jail
definition.
String format
Parameter values, including jail names, can be single tokens or quoted
strings. A token is any sequence of characters that are not considered
special in the syntax of the configuration file (such as a semicolon or
whitespace). If a value contains anything more than letters, numbers,
dots, dashes and underscores, it is advisable to put quote marks around
that value. Either single or double quotes may be used.
Special characters may be quoted by preceding them with a backslash.
Common C-style backslash character codes are also supported, including
control characters and octal or hex ASCII codes. A backslash at the end
of a line will ignore the subsequent newline and continue the string at
the start of the next line.
Variables
A string may use shell-style variable substitution. A parameter or
variable name preceded by a dollar sign, and possibly enclosed in braces,
will be replaced with the value of that parameter or variable. For
example, a jail's path may be defined in terms of its name or hostname:
path = "/var/jail/$name";
path = "/var/jail/${host.hostname}";
Variable substitution occurs in unquoted tokens or in double-quoted
strings, but not in single-quote strings.
A variable is defined in the same way a parameter is, except that the
variable name is preceded with a dollar sign:
$parentdir = "/var/jail";
path = "$parentdir/$name";
The difference between parameters and variables is that variables are
only used for substitution, while parameters are used both for
substitution and for passing to the kernel.
Wildcards
A jail definition with a name of "*" is used to define wildcard
parameters. Every defined jail will contain both the parameters from its
own definition statement, as well as any parameters in a wildcard
definition.
Variable substitution is done on a per-jail basis, even when that
substitution is for a parameter defined in a wildcard section. This is
useful for wildcard parameters based on e.g., a jail's name.
Later definitions in the configuration file supersede earlier ones, so a
wildcard section placed before (above) a jail definition defines
parameters that could be changed on a per-jail basis. Or a wildcard
section placed after (below) all jails would contain parameters that
always apply to every jail. Multiple wildcard statements are allowed,
and wildcard parameters may also be specified outside of a jail
definition statement.
If hierarchical jails are defined, a partial-matching wildcard definition
may be specified. For example, a definition with a name of "foo.*" would
apply to jails with names like "foo.bar" and "foo.bar.baz".
Includes
A line of the form
.include "filename";
will include another file (or files) in the configuration. The filename
should be either absolute, or relative to the configuration file's
directory. It cannot contain variable expansions, but may contain
glob(3) patterns.
The included file must exist, though a filename glob may match zero or
more files. This allows inclusion of any/all files in a directory, such
as "/etc/jail.conf.d/*.conf", or conditional inclusion of a single file,
such as "jail.foo[.]conf".
Comments
The configuration file may contain comments in the common C, C++, and
shell formats:
/* This is a C style comment.
* It may span multiple lines.
*/
// This is a C++ style comment.
# This is a shell style comment.
Comments are legal wherever whitespace is allowed, i.e., anywhere except
in the middle of a string or a token.
FILES
/etc/jail.conf
/etc/jail.*.conf
/etc/jail.conf.d/*.conf
/usr/share/examples/jails/
EXAMPLES
# Typical static defaults:
# Use the rc scripts to start and stop jails. Mount jail's /dev.
exec.start = "/bin/sh /etc/rc";
exec.stop = "/bin/sh /etc/rc.shutdown jail";
exec.clean;
mount.devfs;
# Dynamic wildcard parameter:
# Base the path off the jail name.
path = "/var/jail/$name";
# A typical jail.
foo {
host.hostname = "foo.com";
ip4.addr = 10.1.1.1, 10.1.1.2, 10.1.1.3;
}
# This jail overrides the defaults defined above.
bar {
exec.start = '';
exec.stop = '';
path = /;
mount.nodevfs;
persist; // Required because there are no processes
}
# Include configurations from standard locations.
.include "/etc/jail.conf.d/*.conf";
.include "/etc/jail.*.conf";
.include "/usr/local/etc/jail[.]conf";
.include "/usr/local/etc/jail.conf.d/*.conf";
.include "/usr/local/etc/jail.*.conf";
SEE ALSO
jail(2), jail(3), jail(3lua), rc.conf(5), jail(8), jexec(8), jls(8),
zfs-jail(8)
The "Jails and Containers" chapter of the FreeBSD Handbook.
HISTORY
The jail(8) utility appeared in FreeBSD 4.0. The jail.conf file was
added in FreeBSD 9.1.
AUTHORS
The jail feature was written by Poul-Henning Kamp for R&D Associates who
contributed it to FreeBSD.
James Gritton added the extensible jail parameters and configuration
file.
FreeBSD 15.1-STABLE-HBSD September 21, 2024 JAIL.CONF(5)