2004-11-03 13:51:07 +00:00
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.\" Copyright (C) 2000 by Werner Almesberger
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.\" May be distributed under GPL
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.\"
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.\" Written 2000-02-23 by Werner Almesberger
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2007-09-20 06:52:22 +00:00
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.\" Modified 2004-06-17 Michael Kerrisk <mtk.manpages@gmail.com>
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2004-11-03 13:51:07 +00:00
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.\"
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2007-05-30 05:36:26 +00:00
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.TH PIVOT_ROOT 2 2007-06-01 "Linux" "Linux Programmer's Manual"
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2004-11-03 13:51:07 +00:00
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.SH NAME
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pivot_root \- change the root file system
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.SH SYNOPSIS
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.BI "int pivot_root(const char *" new_root ", const char *" put_old );
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.SH DESCRIPTION
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2007-05-12 09:06:04 +00:00
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.BR pivot_root ()
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moves the root file system of the calling process to the
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2004-11-03 13:51:07 +00:00
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directory \fIput_old\fP and makes \fInew_root\fP the new root file system
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2007-12-27 16:01:37 +00:00
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of the calling process.
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2004-11-03 13:51:07 +00:00
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.\"
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.\" The
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.\" .B CAP_SYS_ADMIN
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.\" capability is required.
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2007-05-12 09:06:04 +00:00
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The typical use of
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.BR pivot_root ()
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is during system startup, when the
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2007-06-08 11:56:22 +00:00
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system mounts a temporary root file system (e.g., an \fBinitrd\fP), then
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2004-11-03 13:51:07 +00:00
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mounts the real root file system, and eventually turns the latter into
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the current root of all relevant processes or threads.
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2007-05-12 09:06:04 +00:00
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.BR pivot_root ()
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may or may not change the current root and the current
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2007-12-27 16:01:37 +00:00
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working directory of any processes or threads which use the old
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2007-04-12 22:42:49 +00:00
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root directory.
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2007-05-12 09:06:04 +00:00
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The caller of
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.BR pivot_root ()
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must ensure that processes with root or current working directory
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at the old root operate correctly in either case.
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An easy way to ensure this is to change their
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2007-12-27 16:01:37 +00:00
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root and current working directory to \fInew_root\fP before invoking
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.BR pivot_root ().
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2004-11-03 13:51:07 +00:00
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The paragraph above is intentionally vague because the implementation
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of
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.BR pivot_root ()
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may change in the future.
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2007-04-12 22:42:49 +00:00
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At the time of writing,
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2007-05-12 09:06:04 +00:00
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.BR pivot_root ()
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changes root and current working directory of each process or
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thread to \fInew_root\fP if they point to the old root directory.
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This
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2004-11-03 13:51:07 +00:00
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is necessary in order to prevent kernel threads from keeping the old
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root directory busy with their root and current working directory,
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even if they never access
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the file system in any way.
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In the future, there may be a mechanism for
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2004-11-03 13:51:07 +00:00
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kernel threads to explicitly relinquish any access to the file system,
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such that this fairly intrusive mechanism can be removed from
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.BR pivot_root ().
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Note that this also applies to the calling process:
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.BR pivot_root ()
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may
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or may not affect its current working directory.
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It is therefore recommended to call
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\fBchdir("/")\fP immediately after
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.BR pivot_root ().
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The following restrictions apply to \fInew_root\fP and \fIput_old\fP:
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.IP \- 3
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They must be directories.
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.IP \- 3
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\fInew_root\fP and \fIput_old\fP must not be on the same file system as
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the current root.
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.IP \- 3
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intro.1, time.1, adjtimex.2, capget.2, eventfd.2, fcntl.2, getrlimit.2, getsockopt.2, gettimeofday.2, intro.2, ioctl_list.2, ioperm.2, mlock.2, pivot_root.2, poll.2, prctl.2, ptrace.2, sched_setscheduler.2, select_tut.2, semget.2, sigaltstack.2, signalfd.2, sysctl.2, timer_settime.2, timerfd_create.2, wait.2, CPU_SET.3, argz_add.3, assert_perror.3, atexit.3, backtrace.3, bcmp.3, clearenv.3, ctime.3, dl_iterate_phdr.3, dlopen.3, ecvt.3, errno.3, error.3, ether_aton.3, exit.3, fenv.3, ferror.3, finite.3, flockfile.3, fnmatch.3, fpathconf.3, fpclassify.3, ftime.3, ftok.3, ftw.3, fwide.3, getaddrinfo.3, gethostbyname.3, getlogin.3, getnameinfo.3, getnetent.3, getopt.3, getprotoent.3, getrpcent.3, getservent.3, glob.3, hsearch.3, inet.3, isalpha.3, iswalnum.3, iswalpha.3, iswblank.3, iswcntrl.3, iswctype.3, iswdigit.3, iswgraph.3, iswlower.3, iswprint.3, iswpunct.3, iswspace.3, iswupper.3, iswxdigit.3, longjmp.3, lsearch.3, malloc.3, matherr.3, mblen.3, mbsinit.3, mbtowc.3, on_exit.3, printf.3, pthread_attr_init.3, pthread_attr_setaffinity_np.3, pthread_attr_setdetachstate.3, pthread_attr_setguardsize.3, pthread_attr_setinheritsched.3, pthread_attr_setschedparam.3, pthread_attr_setschedpolicy.3, pthread_attr_setscope.3, pthread_attr_setstack.3, pthread_attr_setstackaddr.3, pthread_attr_setstacksize.3, pthread_cancel.3, pthread_cleanup_push.3, pthread_equal.3, pthread_getattr_np.3, pthread_getcpuclockid.3, pthread_setaffinity_np.3, pthread_setcancelstate.3, pthread_setconcurrency.3, pthread_setschedparam.3, pthread_setschedprio.3, ptsname.3, putenv.3, putgrent.3, raise.3, rcmd.3, regex.3, rexec.3, rpc.3, rpmatch.3, rtnetlink.3, scandir.3, sem_init.3, setaliasent.3, setbuf.3, setenv.3, setjmp.3, signbit.3, stdio_ext.3, strtod.3, strtol.3, strtoul.3, system.3, termios.3, timeradd.3, tzset.3, ualarm.3, wctomb.3, xdr.3, st.4, tty_ioctl.4, core.5, elf.5, proc.5, bootparam.7, capabilities.7, icmp.7, ip.7, ipv6.7, math_error.7, mdoc.samples.7, mq_overview.7, pthreads.7, raw.7, regex.7, socket.7, tcp.7, tzselect.8: Global fix: s/non-zero/nonzero/
The tendency in English, as prescribed in style guides like
Chicago MoS, is towards removing hyphens after prefixes
like "non-" etc.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2010-01-16 16:40:55 +00:00
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\fIput_old\fP must be underneath \fInew_root\fP, that is, adding a nonzero
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number of \fI/..\fP to the string pointed to by \fIput_old\fP must yield
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the same directory as \fInew_root\fP.
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.IP \- 3
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No other file system may be mounted on \fIput_old\fP.
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.PP
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2007-06-21 22:55:04 +00:00
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See also
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.BR pivot_root (8)
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for additional usage examples.
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2007-06-08 11:56:22 +00:00
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If the current root is not a mount point (e.g., after
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.BR chroot (2)
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or
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.BR pivot_root (),
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see also below), not the old root directory, but the
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mount point of that file system is mounted on \fIput_old\fP.
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2007-05-18 16:06:42 +00:00
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2007-04-12 22:42:49 +00:00
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\fInew_root\fP does not have to be a mount point.
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In this case,
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\fI/proc/mounts\fP will show the mount point of the file system containing
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\fInew_root\fP as root (\fI/\fP).
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.SH "RETURN VALUE"
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On success, zero is returned.
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On error, \-1 is returned, and
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\fIerrno\fP is set appropriately.
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.SH ERRORS
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.BR pivot_root ()
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may return (in \fIerrno\fP) any of the errors returned by
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.BR stat (2).
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Additionally, it may return:
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.TP
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.B EBUSY
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\fInew_root\fP or \fIput_old\fP are on the current root file system,
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or a file system is already mounted on \fIput_old\fP.
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.TP
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.B EINVAL
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\fIput_old\fP is not underneath \fInew_root\fP.
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.TP
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.B ENOTDIR
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\fInew_root\fP or \fIput_old\fP is not a directory.
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.TP
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.B EPERM
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The calling process does not have the
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.B CAP_SYS_ADMIN
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capability.
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2007-05-18 16:06:42 +00:00
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.SH VERSIONS
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.BR pivot_root ()
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was introduced in Linux 2.3.41.
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.SH "CONFORMING TO"
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.BR pivot_root ()
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is Linux-specific and hence is not portable.
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2007-06-14 06:31:39 +00:00
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.SH NOTES
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Glibc does not provide a wrapper for this system call; call it using
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.BR syscall (2).
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.SH BUGS
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.BR pivot_root ()
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should not have to change root and current working directory of all other
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processes in the system.
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2007-05-12 09:06:04 +00:00
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Some of the more obscure uses of
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.BR pivot_root ()
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may quickly lead to
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insanity.
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.SH "SEE ALSO"
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.BR chdir (2),
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.BR chroot (2),
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.BR stat (2),
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.BR initrd (4),
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.BR pivot_root (8)
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