|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
PIVOT_ROOT(2) Linux Programmer's Manual PIVOT_ROOT(2)
pivot_root - change the root filesystem
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 filesystem of the calling process to the
directory put_old and makes new_root the new root filesystem of the
calling process.
The typical use of pivot_root() is during system startup, when the
system mounts a temporary root filesystem (e.g., an initrd), then
mounts the real root filesystem, 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 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 working directory 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 current
working directory, even if they never access the filesystem in any
way. In the future, there may be a mechanism for kernel threads to
explicitly relinquish any access to the filesystem, such that this
fairly intrusive mechanism 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 filesystem 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 filesystem 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 filesystem is mounted on put_old.
new_root does not have to be a mount point. In this case,
/proc/mounts will show the mount point of the filesystem 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 filesystem, or a
filesystem 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 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 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2012-07-13 PIVOT_ROOT(2)
Pages that refer to this page: chroot(2), syscalls(2), initrd(4), pivot_root(8)