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ParaStation5 Administrator's Guide 63
psid
psid — the ParaStation daemon. The organizer of the ParaStation software architecture.
Synopsis
psid [-v?] [-d level] [-f configfile] [-l logfile] [--usage]
Description
The ParaStation daemon is implemented as a Unix daemon process. It supervises allocated resources,
cleans up after application shutdowns, and controls access to common resources. Thus, it takes care of
tasks which are usually managed by the operating system.
The local daemon is usually started by executing psiadmin(1). If it is not running at the time a ParaStation
process is starting, the inetd(8) or xinetd(8) daemon is starting up psid automatically. The daemon can also
be started using the command line. Parameters can be given at the command line or in the configuration file
inetd.conf(5) or xinetd.conf(5). Most of the parameters can also be given in the ParaStation configuration
file parastation.conf(5). As an alternative, the psid can be installed as a service using the start/stop script
/etc/init.d/parastation.
Nodes without a running ParaStation daemon are not visible within the cluster. Be aware of the fact that
psiadmin(1) usually only starts the local daemon. All other daemons managing the nodes configured to
belong to the cluster may be started using the add directive from within the ParaStation administration tool
psiadmin(1).
If psiadmin(1) is started with the -s option, all daemons within the cluster will be started automatically.
The ParaStation daemon must always run with root privileges.
Before a process can communicate with the ParaStation system, it has to register with the daemon. Access
may be granted or denied. The daemon can deny the access due to several reasons:
• the ParaStation system library of the process and the ParaStation daemon are incompatible.
• the daemon is in a state where it does not accept new connections.
• insufficient resources.
• the user is temporally not allowed to access ParaStation (see psiadmin(1)).
• the group is temporally not allowed to access ParaStation (see psiadmin(1)).
• the number of processes exceed the maximum set by psiadmin(1).
The ParaStation daemon can restrict the access to the communication subsystem to a specific user or
a maximum number of processes. This enables the cluster to run in an optimized way, since multiple
processes slow down application execution due to scheduling overhead. (See psiadmin(1), set user, set
group and set maxproc for this features.)
All ParaStation daemons are connected to each other. They exchange local information and transmit
demands of local processes to the psid of the destination node. With this cooperation, the ParaStation
system offers a distributed resource management.
The ParaStation daemon spawns and kills client processes on demand of a parent process. The
ParaStation system transfers remote spawning or killing requests to the daemon of the destination node.
Then operating system functionality is used to spawn and kill the processes on the local node. The spawned
process runs with same user and group id as the spawning process. The ParaStation system redirects the
output of spawned process to the terminal of the parent process.