From 7732f92bad5f24a4bd03bb357af46da56b0ac94d Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Wed, 3 Feb 2016 20:32:06 +0100 Subject: nspawn: optionally run a stub init process as PID 1 This adds a new switch --as-pid2, which allows running commands as PID 2, while a stub init process is run as PID 1. This is useful in order to run arbitrary commands in a container, as PID1's semantics are different from all other processes regarding reaping of unknown children or signal handling. --- man/systemd-nspawn.xml | 65 +++++++++++++++++++++++++++++++++++++++++++++----- man/systemd.nspawn.xml | 24 ++++++++++++------- 2 files changed, 74 insertions(+), 15 deletions(-) (limited to 'man') diff --git a/man/systemd-nspawn.xml b/man/systemd-nspawn.xml index 1cfef93df1..86cdb4e124 100644 --- a/man/systemd-nspawn.xml +++ b/man/systemd-nspawn.xml @@ -248,16 +248,69 @@ . + + + + + Invoke the shell or specified program as process ID (PID) 2 instead of PID 1 (init). By + default, if neither this option nor is used, the selected binary is run as process with + PID 1, a mode only suitable for programs that are aware of the special semantics that the process with PID 1 + has on UNIX. For example, it needs to reap all processes reparented to it, and should implement + sysvinit compatible signal handling (specifically: it needs to reboot on SIGINT, reexecute + on SIGTERM, reload configuration on SIGHUP, and so on). With a minimal stub init + process is run as PID 1 and the selected binary is executed as PID 2 (and hence does not need to implement any + special semantics). The stub init process will reap processes as necessary and react appropriately to + signals. It is recommended to use this mode to invoke arbitrary commands in containers, unless they have been + modified to run correctly as PID 1. Or in other words: this switch should be used for pretty much all commands, + except when the command refers to an init or shell implementation, as these are generally capable of running + correctly as PID 1). This option may not be combined with or + . + + + - Automatically search for an init binary and - invoke it instead of a shell or a user supplied program. If - this option is used, arguments specified on the command line - are used as arguments for the init binary. This option may not - be combined with . - + Automatically search for an init binary and invoke it as PID 1, instead of a shell or a user + supplied program. If this option is used, arguments specified on the command line are used as arguments for the + init binary. This option may not be combined with or + . + + The following table explains the different modes of invocation and relationship to + (see above): + + + Invocation Mode + + + + + + Switch + Explanation + + + + + Neither nor specified + The passed parameters are interpreted as command line, which is executed as PID 1 in the container. + + + + specified + The passed parameters are interpreted as command line, which are executed as PID 2 in the container. A stub init process is run as PID 1. + + + + specified + An init binary as automatically searched and run as PID 1 in the container. The passed parameters are used as invocation parameters for this process. + + + + +
+ diff --git a/man/systemd.nspawn.xml b/man/systemd.nspawn.xml index 7e604246f6..c07a4b0243 100644 --- a/man/systemd.nspawn.xml +++ b/man/systemd.nspawn.xml @@ -141,15 +141,21 @@ Boot= - Takes a boolean argument, which defaults to off. If - enabled, systemd-nspawn will automatically - search for an init executable and invoke - it. In this case, the specified parameters using - Parameters= are passed as additional - arguments to the init process. This - setting corresponds to the switch on - the systemd-nspawn command - line. + Takes a boolean argument, which defaults to off. If enabled, systemd-nspawn + will automatically search for an init executable and invoke it. In this case, the + specified parameters using Parameters= are passed as additional arguments to the + init process. This setting corresponds to the switch on the + systemd-nspawn command line. This option may not be combined with + ProcessTwo=yes. + + + + ProcessTwo= + + Takes a boolean argument, which defaults to off. If enabled, the specified program is run as + PID 2. A stub init process is run as PID 1. This setting corresponds to the switch + on the systemd-nspawn command line. This option may not be combined with + Boot=yes. -- cgit v1.2.3-54-g00ecf