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       setns - reassociate thread with a namespace


       #define _GNU_SOURCE             /* See feature_test_macros(7) */
       #include <sched.h>

       int setns(int fd, int nstype);


       Given  a  file  descriptor  referring  to  a namespace, reassociate the
       calling thread with that namespace.

       The fd argument is a file descriptor referring to one of the  namespace
       entries  in  a  /proc/[pid]/ns/  directory;  see  proc(5)  for  further
       information  on  /proc/[pid]/ns/.    The   calling   thread   will   be
       reassociated   with   the   corresponding  namespace,  subject  to  any
       constraints imposed by the nstype argument.

       The nstype argument specifies  which  type  of  namespace  the  calling
       thread  may  be  reassociated  with.  This argument can have one of the
       following values:

       0      Allow any type of namespace to be joined.

              fd must refer to an IPC namespace.

              fd must refer to a network namespace.

              fd must refer to a UTS namespace.

       Specifying nstype as 0 suffices if the caller knows (or does not  care)
       what  type  of  namespace  is  referred to by fd.  Specifying a nonzero
       value for nstype is useful if the caller does not  know  what  type  of
       namespace  is  referred to by fd and wants to ensure that the namespace
       is of a particular type.  (The caller might not know the  type  of  the
       namespace  referred  to  by  fd  if  the  file descriptor was opened by
       another process and, for example, passed  to  the  caller  via  a  UNIX
       domain socket.)


       On success, setns() returns 0.  On failure, -1 is returned and errno is
       set to indicate the error.


       EBADF  fd is not a valid file descriptor.

       EINVAL fd refers  to  a  namespace  whose  type  does  not  match  that
              specified  in nstype, or there is problem with reassociating the
              the thread with the specified namespace.

       ENOMEM Cannot  allocate  sufficient  memory  to  change  the  specified

       EPERM  The   calling   thread  did  not  have  the  required  privilege
              (CAP_SYS_ADMIN) for this operation.


       The setns() system call first appeared in Linux in kernel 3.0


       The setns() system call is Linux-specific.


       Not all of the attributes that can be  shared  when  a  new  thread  is
       created using clone(2) can be changed using setns().


       The  PID namespace and the mount namespace are not currently supported.
       (See the descriptions of CLONE_NEWPID and CLONE_NEWNS in clone(2).)


       clone(2), fork(2), vfork(2), proc(5), unix(7)


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