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# PCMPIServerBegin
starts a server that runs on the rank != 0 MPI processes waiting to process requests for parallel `KSP` solves and management of parallel `KSP` objects. 
## Synopsis
```
PetscErrorCode PCMPIServerBegin(void)
```
Logically Collective on all MPI ranks except 0


## Options Database Keys

- ***-mpi_linear_solver_server -*** causes the PETSc program to start in MPI linear solver server mode where only the first MPI rank runs user code
- ***-mpi_linear_solver_server_view -*** displays information about the linear systems solved by the MPI linear solver server





## Note
This is normally started automatically in `PetscInitialize()` when the option is provided


## Developer Notes
When called on rank zero this sets `PETSC_COMM_WORLD` to `PETSC_COMM_SELF` to allow a main program
written with `PETSC_COMM_WORLD` to run correctly on the single rank while all the ranks
(that would normally be sharing `PETSC_COMM_WORLD`) to run the solver server.

Can this be integrated into the `PetscDevice` abstraction that is currently being developed?


## See Also
 `PCMPIServerEnd()`, `PCMPI`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/mpi/pcmpi.c.html#PCMPIServerBegin">src/ksp/pc/impls/mpi/pcmpi.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/pc/impls/mpi/pcmpi.c)


[Index of all PC routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)