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PIVOT_ROOT(2)			    Linux Programmer's Manual			    PIVOT_ROOT(2)

       pivot_root - change the root file system

       int pivot_root(const char *new_root, const char *put_old);

       Note: There is no glibc wrapper for this system call; see NOTES.

       pivot_root()  moves  the  root file system of the calling process to the directory put_old
       and makes new_root the new root file system of the calling process.

       The typical use of pivot_root() is during system startup, when the system mounts a  tempo-
       rary  root file system (e.g., an initrd), then mounts the real root file system, and even-
       tually turns the latter into the current root of all relevant processes or threads.

       pivot_root() may or may not change the current root and the current working  directory  of
       any  processes  or  threads  which use the old root directory.  The caller of pivot_root()
       must ensure that processes with root or current working directory at the old root  operate
       correctly  in either case.  An easy way to ensure this is to change their root and current
       working directory to new_root before invoking pivot_root().

       The paragraph above is intentionally vague because the implementation of pivot_root()  may
       change in the future.  At the time of writing, pivot_root() changes root and current work-
       ing directory of each process or thread to new_root if they point to the old  root  direc-
       tory.   This  is  necessary  in	order to prevent kernel threads from keeping the old root
       directory busy with their root and current working directory, even if  they  never  access
       the file system in any way.  In the future, there may be a mechanism for kernel threads to
       explicitly relinquish any access to the file system, such that this fairly intrusive mech-
       anism can be removed from pivot_root().

       Note that this also applies to the calling process: pivot_root() may or may not affect its
       current working directory.  It is therefore recommended	to  call  chdir("/")  immediately
       after pivot_root().

       The following restrictions apply to new_root and put_old:

       -  They must be directories.

       -  new_root and put_old must not be on the same file system as the current root.

       -  put_old  must  be  underneath  new_root, that is, adding a nonzero number of /.. to the
	  string pointed to by put_old must yield the same directory as new_root.

       -  No other file system may be mounted on put_old.

       See also pivot_root(8) for additional usage examples.

       If the current root is not a mount point (e.g., after chroot(2) or pivot_root(), see  also
       below),	not the old root directory, but the mount point of that file system is mounted on

       new_root does not have to be a mount point.  In this  case,  /proc/mounts  will	show  the
       mount point of the file system containing new_root as root (/).

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

       pivot_root()  may  return (in errno) any of the errors returned by stat(2).  Additionally,
       it may return:

       EBUSY  new_root or put_old are on the current root  file  system,  or  a  file  system  is
	      already mounted on put_old.

       EINVAL put_old is not underneath new_root.

	      new_root or put_old is not a directory.

       EPERM  The calling process does not have the CAP_SYS_ADMIN capability.

       pivot_root() was introduced in Linux 2.3.41.

       pivot_root() is Linux-specific and hence is not portable.

       Glibc does not provide a wrapper for this system call; call it using syscall(2).

       pivot_root()  should  not  have	to change root and current working directory of all other
       processes in the system.

       Some of the more obscure uses of pivot_root() may quickly lead to insanity.

       chdir(2), chroot(2), stat(2), initrd(4), pivot_root(8)

       This page is part of release 3.53 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at

Linux					    2012-07-13				    PIVOT_ROOT(2)
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