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RedHat 9 (Linux i386) - man page for pivot_root (redhat section 2)

PIVOT_ROOT(2)				   System Calls 			    PIVOT_ROOT(2)

NAME
       pivot_root - change the root file system

SYNOPSIS
       #include <linux/unistd.h>

       _syscall2(int,pivot_root,const char *,new_root,const char *,put_old)

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

DESCRIPTION
       pivot_root  moves the root file system of the current process to the directory put_old and
       makes new_root the new root file system of the current process.

       The typical use of pivot_root is during system startup, when the system mounts a temporary
       root  file  system (e.g. an initrd), then mounts the real root file system, and eventually
       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  (cwd)
       of  any	processes  or  threads which use the old root directory. The caller of pivot_root
       must ensure that processes with root or cwd at the old root operate  correctly  in  either
       case. An easy way to ensure this is to change their root and cwd to new_root before invok-
       ing 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 cwd of each
       process or thread to new_root if they point to the old root directory. This  is	necessary
       in  order  to  prevent  kernel threads from keeping the old root directory busy with their
       root and cwd, 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 sys-
       tem, such that this fairly intrusive mechanism can be removed from pivot_root.

       Note that this also applies to the current process: pivot_root may or may not  affect  its
       cwd. 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, i.e. adding a non-zero 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
       put_old.

NOTES
       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 (/).

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

ERRORS
       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.

       ENOTDIR
	      new_root or put_old is not a directory.

       EPERM  The current process does not have the administrator capability.

BUGS
       pivot_root should not have to change root and cwd of all other processes in the system.

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

CONFORMING TO
       pivot_root is Linux-specific and hence is not portable.

HISTORY
       pivot_root was introduced in Linux 2.3.41.

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

Linux					    2000-02-23				    PIVOT_ROOT(2)


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