2015-03-21 21:19:06 +00:00
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.\" Copyright (c) 2015 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\"
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.\"
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ldd.1, sprof.1, accept.2, alarm.2, bind.2, chdir.2, clock_nanosleep.2, close.2, connect.2, dup.2, execve.2, fsync.2, getgid.2, getpeername.2, getsid.2, getsockname.2, getsockopt.2, getuid.2, io_getevents.2, kill.2, listen.2, lseek.2, mmap.2, msgctl.2, msgget.2, msgop.2, msync.2, nanosleep.2, nice.2, pause.2, pipe.2, rmdir.2, sched_get_priority_max.2, sched_rr_get_interval.2, sched_setparam.2, sched_setscheduler.2, sched_yield.2, select_tut.2, semctl.2, semop.2, setsid.2, shmctl.2, shmget.2, shmop.2, shutdown.2, sigaction.2, signal.2, socketpair.2, sync.2, timer_delete.2, timer_getoverrun.2, timer_settime.2, times.2, truncate.2, umask.2, MB_CUR_MAX.3, a64l.3, abs.3, assert.3, atexit.3, atof.3, atoi.3, basename.3, bsearch.3, btowc.3, byteorder.3, catgets.3, catopen.3, clock.3, clock_getcpuclockid.3, closedir.3, confstr.3, crypt.3, ctermid.3, difftime.3, div.3, dladdr.3, dlerror.3, dlinfo.3, dlopen.3, dlsym.3, drand48.3, encrypt.3, exit.3, fclose.3, ffs.3, fgetc.3, fgetwc.3, fgetws.3, flockfile.3, fmtmsg.3, fnmatch.3, fopen.3, fpathconf.3, fpclassify.3, fputwc.3, fputws.3, fseek.3, fseeko.3, ftok.3, fwide.3, getdate.3, getenv.3, getgrent.3, getgrnam.3, gethostid.3, getlogin.3, getnetent.3, getopt.3, getpwent.3, getpwnam.3, getsubopt.3, getutent.3, getwchar.3, grantpt.3, hsearch.3, iconv.3, iconv_close.3, iconv_open.3, if_nameindex.3, inet.3, inet_ntop.3, inet_pton.3, insque.3, isatty.3, isgreater.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, lockf.3, longjmp.3, lsearch.3, malloc.3, mblen.3, mbrlen.3, mbrtowc.3, mbsinit.3, mbsrtowcs.3, mbstowcs.3, mbtowc.3, memccpy.3, memchr.3, memcmp.3, memmove.3, memset.3, mktemp.3, mq_close.3, mq_getattr.3, mq_receive.3, mq_send.3, mq_unlink.3, offsetof.3, popen.3, posix_memalign.3, posix_openpt.3, printf.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_setstacksize.3, pthread_equal.3, pthread_exit.3, pthread_getcpuclockid.3, pthread_kill.3, pthread_self.3, pthread_setcancelstate.3, pthread_setconcurrency.3, pthread_setschedparam.3, pthread_setschedprio.3, pthread_sigmask.3, pthread_testcancel.3, ptsname.3, putenv.3, puts.3, putwchar.3, qsort.3, raise.3, random.3, readdir.3, regex.3, remove.3, rewinddir.3, seekdir.3, sem_destroy.3, sem_getvalue.3, sem_unlink.3, sem_wait.3, setenv.3, setjmp.3, setlocale.3, setlogmask.3, signbit.3, sigpause.3, sigset.3, sigsetops.3, sigwait.3, sleep.3, sockatmark.3, statvfs.3, strcat.3, strchr.3, strcmp.3, strcoll.3, strcpy.3, strlen.3, strpbrk.3, strptime.3, strspn.3, strstr.3, strtod.3, strtoimax.3, strtok.3, strtol.3, strtoul.3, strxfrm.3, swab.3, sysconf.3, system.3, tcgetpgrp.3, tcgetsid.3, telldir.3, tmpfile.3, towctrans.3, tsearch.3, ttyname.3, tzset.3, ungetwc.3, unlocked_stdio.3, unlockpt.3, wcrtomb.3, wcscat.3, wcschr.3, wcscmp.3, wcscpy.3, wcscspn.3, wcslen.3, wcsncat.3, wcsncmp.3, wcsncpy.3, wcspbrk.3, wcsrchr.3, wcsrtombs.3, wcsspn.3, wcsstr.3, wcstoimax.3, wcstok.3, wcstombs.3, wcswidth.3, wctob.3, wctomb.3, wctrans.3, wctype.3, wcwidth.3, wmemchr.3, wmemcmp.3, wmemcpy.3, wmemmove.3, wmemset.3, wordexp.3, wprintf.3, fanotify.7, mq_overview.7, nptl.7, sem_overview.7, shm_overview.7, sigevent.7, symlink.7, ld.so.8: tstamp
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2015-08-08 16:21:22 +00:00
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.TH NPTL 7 2015-08-08 "Linux" "Linux Programmer's Manual"
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2015-03-21 21:19:06 +00:00
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.SH NAME
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nptl \- Native POSIX Threads Library
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.SH DESCRIPTION
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NPTL (Native POSIX Threads Library)
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is the GNU C library POSIX threads implementation that is used on modern
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Linux systems.
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.\"
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.SS NPTL and signals
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NPTL makes internal use of the first two real-time signals
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(signal numbers 32 and 33).
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2015-04-06 07:58:16 +00:00
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One of these signals is used to support thread cancellation and POSIX timers
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(see
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.BR timer_create (2));
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2015-03-21 21:19:06 +00:00
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the other is used as part of a mechanism that ensures all threads in
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a process always have the same UIDs and GIDs, as required by POSIX.
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These signals cannot be used in applications.
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aio.7, arp.7, attributes.7, boot.7, cgroups.7, cpuset.7, credentials.7, fanotify.7, fifo.7, glob.7, hier.7, hostname.7, icmp.7, inode.7, inotify.7, keyrings.7, libc.7, mailaddr.7, mount_namespaces.7, mq_overview.7, nptl.7, numa.7, path_resolution.7, persistent-keyring.7, pid_namespaces.7, pipe.7, pkeys.7, process-keyring.7, pthreads.7, pty.7, random.7, sched.7, sem_overview.7, session-keyring.7, shm_overview.7, signal-safety.7, signal.7, spufs.7, standards.7, symlink.7, termio.7, thread-keyring.7, time.7, unicode.7, user-keyring.7, user-session-keyring.7, user_namespaces.7, utf-8.7, xattr.7: ffix
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2017-08-17 22:59:04 +00:00
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.PP
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2015-03-21 21:19:06 +00:00
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To prevent accidental use of these signals in applications,
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which might interfere with the operation of the NPTL implementation,
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various glibc library functions and system call wrapper functions
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attempt to hide these signals from applications,
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as follows:
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.IP * 3
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.B SIGRTMIN
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is defined with the value 34 (rather than 32).
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.IP *
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The
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.BR sigwaitinfo (2),
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.BR sigtimedwait (2),
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and
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.BR sigwait (3)
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interfaces silently ignore requests to wait for these two signals
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if they are specified in the signal set argument of these calls.
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.IP *
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The
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.BR sigprocmask (2)
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and
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.BR pthread_sigmask (3)
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interfaces silently ignore attempts to block these two signals.
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.IP *
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The
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.BR sigaction (2),
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.BR pthread_kill (3),
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and
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.BR pthread_sigqueue (3)
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interfaces fail with the error
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.B EINVAL
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(indicating an invalid signal number) if these signals are specified.
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.IP *
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.BR sigfillset (3)
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does not include these two signals when it creates a full signal set.
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.\"
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.SS NPTL and process credential changes
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At the Linux kernel level,
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credentials (user and group IDs) are a per-thread attribute.
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However, POSIX requires that all of the POSIX threads in a process
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have the same credentials.
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To accommodate this requirement,
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the NPTL implementation wraps all of the system calls that
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change process credentials with functions that,
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in addition to invoking the underlying system call,
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arrange for all other threads in the process to also change their credentials.
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aio.7, arp.7, attributes.7, boot.7, cgroups.7, cpuset.7, credentials.7, fanotify.7, fifo.7, glob.7, hier.7, hostname.7, icmp.7, inode.7, inotify.7, keyrings.7, libc.7, mailaddr.7, mount_namespaces.7, mq_overview.7, nptl.7, numa.7, path_resolution.7, persistent-keyring.7, pid_namespaces.7, pipe.7, pkeys.7, process-keyring.7, pthreads.7, pty.7, random.7, sched.7, sem_overview.7, session-keyring.7, shm_overview.7, signal-safety.7, signal.7, spufs.7, standards.7, symlink.7, termio.7, thread-keyring.7, time.7, unicode.7, user-keyring.7, user-session-keyring.7, user_namespaces.7, utf-8.7, xattr.7: ffix
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2017-08-17 22:59:04 +00:00
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.PP
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2015-03-29 20:31:35 +00:00
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The implementation of each of these system calls involves the use of
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2015-03-21 21:19:06 +00:00
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a real-time signal that is sent (using
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.BR tgkill (2))
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2015-03-22 19:00:44 +00:00
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to each of the other threads that must change its credentials.
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2015-03-21 21:19:06 +00:00
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Before sending these signals, the thread that is changing credentials
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saves the new credential(s) and records the system call being employed
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in a global buffer.
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A signal handler in the receiving thread(s) fetches this information and
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then uses the same system call to change its credentials.
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aio.7, arp.7, attributes.7, boot.7, cgroups.7, cpuset.7, credentials.7, fanotify.7, fifo.7, glob.7, hier.7, hostname.7, icmp.7, inode.7, inotify.7, keyrings.7, libc.7, mailaddr.7, mount_namespaces.7, mq_overview.7, nptl.7, numa.7, path_resolution.7, persistent-keyring.7, pid_namespaces.7, pipe.7, pkeys.7, process-keyring.7, pthreads.7, pty.7, random.7, sched.7, sem_overview.7, session-keyring.7, shm_overview.7, signal-safety.7, signal.7, spufs.7, standards.7, symlink.7, termio.7, thread-keyring.7, time.7, unicode.7, user-keyring.7, user-session-keyring.7, user_namespaces.7, utf-8.7, xattr.7: ffix
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2017-08-17 22:59:04 +00:00
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.PP
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2015-03-21 21:19:06 +00:00
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Wrapper functions employing this technique are provided for
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.BR setgid (2),
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.BR setuid (2),
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.BR setegid (2),
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.BR seteuid (2),
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.BR setregid (2),
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.BR setreuid (2),
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.BR setresgid (2),
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.BR setresuid (2),
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and
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.BR setgroups (2).
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2015-07-24 07:55:21 +00:00
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.\" FIXME .
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.\" Maybe say something about vfork() not being serialized wrt set*id() APIs?
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.\" https://sourceware.org/bugzilla/show_bug.cgi?id=14749
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2015-03-21 21:19:06 +00:00
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.SH CONFORMING TO
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For details of the conformance of NPTL to the POSIX standard, see
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.BR pthreads (7).
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2015-07-26 20:27:20 +00:00
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.SH NOTES
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POSIX says
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.\" See POSIX.1-2008 specification of pthread_mutexattr_init()
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that any thread in any process with access to the memory
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containing a process-shared
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.RB ( PTHREAD_PROCESS_SHARED )
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mutex can operate on that mutex.
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However, on 64-bit x86 systems, the mutex definition for x86-64
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is incompatible with the mutex definition for i386,
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.\" See sysdeps/x86/bits/pthreadtypes.h
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meaning that 32-bit and 64-bit binaries can't share mutexes on x86-64 systems.
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2015-03-21 21:19:06 +00:00
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.SH SEE ALSO
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.BR credentials (7),
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.BR pthreads (7),
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.BR signal (7),
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.BR standards (7)
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