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Intro(2)			 System Calls			      Intro(2)

NAME
       Intro, intro - introduction to system calls and error numbers

SYNOPSIS
       #include <errno.h>

DESCRIPTION
       A  system call is a C library function that requests a service from the
       system, such as getting the time of day. This request is	 performed  in
       the  kernel.  The  library  interface  executes a trap into the kernel,
       which actually executes the system call code.

       Most system calls return one or more error conditions. An error	condi‐
       tion  is	 indicated  by	an  otherwise impossible return value. This is
       almost always −1 or the null pointer; the individual descriptions spec‐
       ify the details. An error number is also made available in the external
       variable errno, which is not cleared on successful calls, so it	should
       be tested only after an error has been indicated.

       In the case of multithreaded applications, the -mt option must be spec‐
       ified on the command line at compilation time  (see  threads(5)).  When
       the  -mt	 option	 is specified, errno becomes a macro that enables each
       thread to have its own errno. This errno macro can be  used  on	either
       side of the assignment as though it were a variable.

       An error value listed as "will fail" describes a condition whose detec‐
       tion and reporting is mandatory for an implementation that conforms  to
       the  Single  UNIX  Specification (SUS). An application can rely on this
       condition being detected and reported. An error value  listed  as  "may
       fail"  describes a condition whose detection and reporting is  optional
       for an implementation that conforms to the SUS. An  application	should
       not  rely  this	condition  being detected and reported. An application
       that relies on such behavior cannot be assured to  be  portable	across
       conforming implementations. If more than one error occurs in processing
       a function call, any one of the possible errors might may be  returned,
       as the order of detection is undefined. See standards(5) for additional
       information regarding the Single UNIX Specification.

       Each system call description attempts to list all possible  error  num‐
       bers.  The  following is a complete list of the error numbers and their
       names as defined in <errno.h>.

       1 EPERM		      Lacking appropriate privileges

			      Typically this error  indicates  an  attempt  to
			      modify  a	 file  in some way forbidden except to
			      its  owner  or   an   appropriately   privileged
			      process.	 It  is	 also returned for attempts by
			      ordinary users  to  perform  operations  allowed
			      only to processes with certain privileges.

			      The  manual pages for individual functions docu‐
			      ment which privileges are needed to override the
			      restriction.

       2 ENOENT		      No such file or directory

			      A	 file  name  is	 specified and the file should
			      exist but doesn't, or one of the directories  in
			      a path name does not exist.

       3 ESRCH		      No such process, LWP, or thread

			      No  process can be found in the system that cor‐
			      responds	to  the	 specified  PID,  LWPID_t,  or
			      thread_t.

       4 EINTR		      Interrupted system call

			      An  asynchronous	signal	(such  as interrupt or
			      quit), which the	user  has  elected  to	catch,
			      occurred	during	a  system service function. If
			      execution is resumed after processing  the  sig‐
			      nal,  it will appear as if the interrupted func‐
			      tion call returned this error condition.

			      In a multithreaded  application,	EINTR  may  be
			      returned	whenever  another  thread or LWP calls
			      fork(2).

       5 EIO		      I/O error

			      Some physical I/O error has occurred. This error
			      may  in some cases occur on a call following the
			      one to which it actually applies.

       6 ENXIO		      No such device or address

			      I/O on a special	file  refers  to  a  subdevice
			      which does not exist, or exists beyond the limit
			      of the device. It may also occur when, for exam‐
			      ple, a tape drive is not on-line or no disk pack
			      is loaded on a drive.

       7 E2BIG		      Arg list too long

			      An argument list longer than  ARG_MAX  bytes  is
			      presented	 to  a	member	of  the exec family of
			      functions (see exec(2)). The argument list limit
			      is the sum of the size of the argument list plus
			      the size of  the	environment's  exported	 shell
			      variables.

       8 ENOEXEC	      Exec format error

			      A	 request  is  made  to	execute	 a file which,
			      although it  has	the  appropriate  permissions,
			      does   not   start  with	a  valid  format  (see
			      a.out(4)).

       9 EBADF		      Bad file number

			      Either a file descriptor refers to no open file,
			      or  a  read(2) (respectively,  write(2)) request
			      is made to a file that is open only for  writing
			      (respectively, reading).

       10 ECHILD	      No child processes

			      A	 wait(3C)  function  call  was	executed  by a
			      process that had	no  existing  or  unwaited-for
			      child processes.

       11 EAGAIN	      No more processes, or no more LWPs

			      For example, the fork(2) function failed because
			      the system's process table is full or  the  user
			      is  not allowed to create any more processes, or
			      a call failed because of insufficient memory  or
			      swap space.

       12 ENOMEM	      Not enough space

			      During   execution   of  brk()  or  sbrk()  (see
			      brk(2)), or one of the exec family of functions,
			      a program asks for more space than the system is
			      able to supply. This is not a  temporary	condi‐
			      tion; the maximum size is a system parameter. On
			      some architectures, the error may also occur  if
			      the  arrangement	of  text, data, and stack seg‐
			      ments requires too many segmentation  registers,
			      or  if there is not enough swap space during the
			      fork(2) function.

       13 EACCES	      Permission denied

			      An attempt was made to access a file  in	a  way
			      forbidden by the protection system.

			      The  manual pages for individual functions docu‐
			      ment which privileges are needed to override the
			      protection system.

       14 EFAULT	      Bad address

			      The  system  encountered	a  hardware  fault  in
			      attempting to use an argument of a routine.  For
			      example, errno potentially may be set to	EFAULT
			      any time a routine that takes a pointer argument
			      is  passed an invalid address, if the system can
			      detect the condition. Because systems will  dif‐
			      fer  in  their  ability to reliably detect a bad
			      address, on some implementations passing	a  bad
			      address  to  a  routine will result in undefined
			      behavior.

       15 ENOTBLK	      Block device required

			      A non-block device or file was mentioned where a
			      block  device  was  required  (for example, in a
			      call to the mount(2) function).

       16 EBUSY		      Device busy

			      An attempt was made to mount a device  that  was
			      already  mounted	or  an	attempt	 was  made  to
			      unmount a device on which	 there	is  an	active
			      file  (open  file, current directory, mounted-on
			      file, active text segment). It will  also	 occur
			      if  an attempt is made to enable accounting when
			      it is already enabled. The device or resource is
			      currently	 unavailable.	 EBUSY is also used by
			      mutexes, semaphores,  condition  variables,  and
			      r/w  locks,  to  indicate	 that  a lock is held,
			      and by the processor control function  P_ONLINE.

       17 EEXIST	      File exists

			      An existing file was mentioned in an inappropri‐
			      ate  context  (for  example, call to the link(2)
			      function).

       18 EXDEV		      Cross-device link

			      A hard link to a	file  on  another  device  was
			      attempted.

       19 ENODEV	      No such device

			      An  attempt  was	made to apply an inappropriate
			      operation to  a  device  (for  example,  read  a
			      write-only device).

       20 ENOTDIR	      Not a directory

			      A	 non-directory was specified where a directory
			      is required (for example, in a path prefix or as
			      an argument to the chdir(2) function).

       21 EISDIR	      Is a directory

			      An attempt was made to write on a directory.

       22 EINVAL	      Invalid argument

			      An  invalid argument was specified (for example,
			      unmounting a non-mounted device), mentioning  an
			      undefined	 signal in a call to the signal(3C) or
			      kill(2) function, or  an	unsupported  operation
			      related to extended attributes was attempted.

       23 ENFILE	      File table overflow

			      The   system   file  table  is  full  (that  is,
			      SYS_OPEN files are open, and temporarily no more
			      files can be opened).

       24 EMFILE	      Too many open files

			      No  process  may	have  more than	 OPEN_MAX file
			      descriptors open at a time.

       25 ENOTTY	      Inappropriate ioctl for device

			      A call was made to the ioctl(2) function	speci‐
			      fying  a	file  that  is not a special character
			      device.

       26 ETXTBSY	      Text file busy (obsolete)

			      An attempt was made to execute a	pure-procedure
			      program that is currently open for writing. Also
			      an attempt to open for writing or	 to  remove  a
			      pure-procedure  program  that is being executed.
			      (This message is obsolete.)

       27 EFBIG		      File too large

			      The size of the file exceeded the	 limit	speci‐
			      fied  by	resource  RLIMIT_FSIZEn; the file size
			      exceeds the maximum supported by the  file  sys‐
			      tem; or the file size exceeds the offset maximum
			      of the file descriptor.  See the File Descriptor
			      subsection of the DEFINITIONS section below.

       28 ENOSPC	      No space left on device

			      While  writing  an  ordinary  file or creating a
			      directory entry, there is no free space left  on
			      the  device.  In the fcntl(2) function, the set‐
			      ting or removing of record locks on a file  can‐
			      not  be  accomplished  because there are no more
			      record entries left on the system.

       29 ESPIPE	      Illegal seek

			      A call to the  lseek(2) function was issued to a
			      pipe.

       30 EROFS		      Read-only file system

			      An  attempt  to  modify  a file or directory was
			      made on a device mounted read-only.

       31 EMLINK	      Too many links

			      An attempt to make more than the maximum	number
			      of links,	 LINK_MAX, to a file.

       32 EPIPE		      Broken pipe

			      A	 write on a pipe for which there is no process
			      to read the data. This condition normally gener‐
			      ates a signal; the error is returned if the sig‐
			      nal is ignored.

       33 EDOM		      Math argument out of domain of function

			      The argument of a function in the	 math  package
			      (3M) is out of the domain of the function.

       34 ERANGE	      Math result not representable

			      The value of a function in the math package (3M)
			      is not representable within machine precision.

       35 ENOMSG	      No message of desired type

			      An attempt was made to receive a	message	 of  a
			      type  that  does not exist on the specified mes‐
			      sage queue (see msgrcv(2)).

       36 EIDRM		      Identifier removed

			      This error is returned to processes that	resume
			      execution	 due  to  the removal of an identifier
			      from  the	 file	system's   name	  space	  (see
			      msgctl(2), semctl(2), and shmctl(2)).

       37 ECHRNG	      Channel number out of range

       38 EL2NSYNC	      Level 2 not synchronized

       39 EL3HLT	      Level 3 halted

       40 EL3RST	      Level 3 reset

       41 ELNRNG	      Link number out of range

       42 EUNATCH	      Protocol driver not attached

       43 ENOCSI	      No CSI structure available

       44 EL2HLT	      Level 2 halted

       45 EDEADLK	      Deadlock condition

			      A	 deadlock  situation was detected and avoided.
			      This error pertains to file and record  locking,
			      and  also applies to mutexes, semaphores, condi‐
			      tion variables, and r/w locks.

       46 ENOLCK	      No record locks available

			      There are no more locks  available.  The	system
			      lock table is full (see fcntl(2)).

       47 ECANCELED	      Operation canceled

			      The  associated  asynchronous operation was can‐
			      celed before completion.

       48 ENOTSUP	      Not supported

			      This version of the system does not support this
			      feature.	Future versions of the system may pro‐
			      vide support.

       49 EDQUOT	      Disc quota exceeded

			      A write(2) to an ordinary file, the creation  of
			      a directory or symbolic link, or the creation of
			      a directory  entry  failed  because  the	user's
			      quota of disk blocks was exhausted, or the allo‐
			      cation of an inode  for  a  newly	 created  file
			      failed  because  the  user's quota of inodes was
			      exhausted.

       58-59		      Reserved

       60 ENOSTR	      Device not a stream

			      A putmsg(2) or getmsg(2) call was attempted on a
			      file descriptor that is not a STREAMS device.

       61 ENODATA	      No data available

       62 ETIME		      Timer expired

			      The  timer  set  for a STREAMS ioctl(2) call has
			      expired. The cause of this error is  device-spe‐
			      cific  and  could	 indicate either a hardware or
			      software failure, or  perhaps  a	timeout	 value
			      that  is	too  short for the specific operation.
			      The status of the ioctl() operation is  indeter‐
			      minate.  This  is	 also  returned in the case of
			      _lwp_cond_timedwait(2) or cond_timedwait(3C).

       63 ENOSR		      Out of stream resources

			      During  a	  STREAMS  open(2)  call,  either   no
			      STREAMS  queues  or  no STREAMS head data struc‐
			      tures were available. This is a temporary condi‐
			      tion; one may recover from it if other processes
			      release resources.

       65 ENOPKG	      Package not installed

			      This error occurs when users attempt  to	use  a
			      call   from   a	package	 which	has  not  been
			      installed.

       71 EPROTO	      Protocol error

			      Some protocol error  occurred.   This  error  is
			      device-specific, but is generally not related to
			      a hardware failure.

       77 EBADMSG	      Not a data message

			      During  a	 read(2),   getmsg(2),	 or   ioctl(2)
			      I_RECVFD call to a STREAMS device, something has
			      come to the head of the queue that  can  not  be
			      processed.  That something depends on the call:

			      read():	   control  information or passed file
					   descriptor.

			      getmsg():	   passed file descriptor.

			      ioctl():	   control or data information.

       78 ENAMETOOLONG	      File name too long

			      The  length  of  the   path   argument   exceeds
			      PATH_MAX,	 or  the  length  of  a path component
			      exceeds NAME_MAX	while  _POSIX_NO_TRUNC	is  in
			      effect; see limits.h(3HEAD).

       79 EOVERFLOW	      Value too large for defined data type.

       80 ENOTUNIQ	      Name not unique on network

			      Given log name not unique.

       81 EBADFD	      File descriptor in bad state

			      Either  a file descriptor refers to no open file
			      or a read request was made to  a	file  that  is
			      open only for writing.

       82 EREMCHG	      Remote address changed

       83 ELIBACC	      Cannot access a needed share library

			      Trying  to  exec an a.out that requires a static
			      shared library and  the  static  shared  library
			      does not exist or the user does not have permis‐
			      sion to use it.

       84 ELIBBAD	      Accessing a corrupted shared library

			      Trying to exec an a.out that requires  a	static
			      shared  library (to be linked in) and exec could
			      not load the static shared library.  The	static
			      shared library is probably corrupted.

       85 ELIBSCN	      .lib section in a.out corrupted

			      Trying  to  exec an a.out that requires a static
			      shared library (to be linked in) and  there  was
			      erroneous data in the .lib section of the a.out.
			      The .lib section tells exec what	static	shared
			      libraries are needed. The a.out is probably cor‐
			      rupted.

       86 ELIBMAX	      Attempting to link in more shared libraries than
			      system limit

			      Trying  to  exec	an  a.out  that	 requires more
			      static shared libraries than is allowed  on  the
			      current  configuration of the system. See System
			      Administration Guide: IP Services

       87 ELIBEXEC	      Cannot exec a shared library directly

			      Attempting to exec a shared library directly.

       88 EILSEQ	      Error 88

			      Illegal byte sequence. Handle  multiple  charac‐
			      ters as a single character.

       89 ENOSYS	      Operation not applicable

       90 ELOOP		      Number of symbolic links encountered during path
			      name traversal exceeds MAXSYMLINKS

       91 ESTART	      Restartable system call

			      Interrupted system call should be restarted.

       92 ESTRPIPE	      If pipe/FIFO, don't sleep in stream head

			      Streams pipe error (not externally visible).

       93 ENOTEMPTY	      Directory not empty

       94 EUSERS	      Too many users

       95 ENOTSOCK	      Socket operation on non-socket

       96 EDESTADDRREQ	      Destination address required

			      A required address was omitted from an operation
			      on  a  transport	endpoint.  Destination address
			      required.

       97 EMGSIZE	      Message too long

			      A message	 sent  on  a  transport	 provider  was
			      larger  than the internal message buffer or some
			      other network limit.

       98 EPROTOTYPE	      Protocol wrong type for socket

			      A protocol was specified that does  not  support
			      the semantics of the socket type requested.

       99 ENOPROTOOPT	      Protocol not available

			      A bad option or level was specified when getting
			      or setting options for a protocol.

       120 EPROTONOSUPPORT    Protocol not supported

			      The protocol has not been	 configured  into  the
			      system or no implementation for it exists.

       121 ESOCKTNOSUPPORT    Socket type not supported

			      The  support  for	 the  socket type has not been
			      configured into the system or no	implementation
			      for it exists.

       122 EOPNOTSUPP	      Operation not supported on transport endpoint

			      For  example, trying to accept a connection on a
			      datagram transport endpoint.

       123 EPFNOSUPPORT	      Protocol family not supported

			      The protocol family has not been configured into
			      the  system  or no implementation for it exists.
			      Used for the Internet protocols.

       124 EAFNOSUPPORT	      Address family not supported by protocol family

			      An address incompatible with the requested  pro‐
			      tocol was used.

       125 EADDRINUSE	      Address already in use

			      User attempted to use an address already in use,
			      and the protocol does not allow this.

       126 EADDRNOTAVAIL      Cannot assign requested address

			      Results from an attempt to  create  a  transport
			      endpoint	with  an  address  not	on the current
			      machine.

       127 ENETDOWN	      Network is down

			      Operation encountered a dead network.

       128 ENETUNREACH	      Network is unreachable

			      Operation was attempted to an  unreachable  net‐
			      work.

       129 ENETRESET	      Network dropped connection because of reset

			      The  host	 you  were  connected  to  crashed and
			      rebooted.

       130 ECONNABORTED	      Software caused connection abort

			      A connection abort was caused internal  to  your
			      host machine.

       131 ECONNRESET	      Connection reset by peer

			      A connection was forcibly closed by a peer. This
			      normally results from a loss of  the  connection
			      on the remote host due to a timeout or a reboot.

       132 ENOBUFS	      No buffer space available

			      An operation on a transport endpoint or pipe was
			      not performed because the system	lacked	suffi‐
			      cient buffer space or because a queue was full.

       133 EISCONN	      Transport endpoint is already connected

			      A	 connect  request  was made on an already con‐
			      nected transport endpoint; or, a sendto(3SOCKET)
			      or   sendmsg(3SOCKET)  request  on  a  connected
			      transport endpoint specified a destination  when
			      already connected.

       134 ENOTCONN	      Transport endpoint is not connected

			      A request to send or receive data was disallowed
			      because the transport endpoint is not  connected
			      and  (when  sending  a  datagram) no address was
			      supplied.

       143 ESHUTDOWN	      Cannot send after transport endpoint shutdown

			      A request to send data  was  disallowed  because
			      the  transport  endpoint	has  already been shut
			      down.

       144 ETOOMANYREFS	      Too many references: cannot splice

       145 ETIMEDOUT	      Connection timed out

			      A	 connect(3SOCKET)  or	send(3SOCKET)  request
			      failed because the connected party did not prop‐
			      erly respond  after  a  period  of  time;	 or  a
			      write(2)	or  fsync(3C) request failed because a
			      file is on an  NFS file system mounted with  the
			      soft option.

       146 ECONNREFUSED	      Connection refused

			      No  connection  could be made because the target
			      machine  actively	 refused  it.	This   usually
			      results from trying to connect to a service that
			      is inactive on the remote host.

       147 EHOSTDOWN	      Host is down

			      A transport provider  operation  failed  because
			      the destination host was down.

       148 EHOSTUNREACH	      No route to host

			      A	 transport provider operation was attempted to
			      an unreachable host.

       149 EALREADY	      Operation already in progress

			      An operation was	attempted  on  a  non-blocking
			      object   that   already	had  an	 operation  in
			      progress.

       150 EINPROGRESS	      Operation now in progress

			      An operation that takes a long time to  complete
			      (such  as	 a  connect()) was attempted on a non-
			      blocking object.

       151 ESTALE	      Stale NFS file handle

DEFINITIONS
   Background Process Group
       Any process group that is not the foreground process group  of  a  ses‐
       sion that has established a connection with a controlling terminal.

   Controlling Process
       A  session leader that established a connection to a controlling termi‐
       nal.

   Controlling Terminal
       A terminal that is associated with a session.  Each session  may	 have,
       at  most, one controlling terminal associated with it and a controlling
       terminal may be	associated  with  only	one  session.	Certain	 input
       sequences  from	the  controlling  terminal cause signals to be sent to
       process groups in the session associated with the controlling terminal;
       see termio(7I).

   Directory
       Directories organize files into a hierarchical system where directories
       are the nodes in the hierarchy. A directory is a file that catalogs the
       list  of	 files,	 including  directories	 (sub-directories),  that  are
       directly beneath it in the hierarchy. Entries in a directory  file  are
       called  links.  A link associates a file identifier with a filename. By
       convention, a directory contains at least two links,  .	(dot)  and  ..
       (dot-dot).  The	link  called  dot refers to the directory itself while
       dot-dot refers to its parent directory. The root	 directory,  which  is
       the top-most node of the hierarchy, has itself as its parent directory.
       The pathname of the root directory is / and the parent directory of the
       root directory is /.

   Downstream
       In a stream, the direction from stream head to driver.

   Driver
       In a stream, the driver provides the interface between peripheral hard‐
       ware and the stream. A driver can also be a pseudo-driver,  such	 as  a
       multiplexor or log driver (see log(7D)), which is not associated with a
       hardware device.

   Effective User ID and Effective Group ID
       An active process has an effective user ID and an  effective  group  ID
       that  are  used	to  determine file access permissions (see below). The
       effective user ID and effective group ID are  equal  to	the  process's
       real user ID and real group ID, respectively, unless the process or one
       of its ancestors evolved from a file that had the  set-user-ID  bit  or
       set-group-ID bit set  (see exec(2)).

   File Access Permissions
       Read, write, and execute/search permissions for a file are granted to a
       process if one or more of the following are true:

	   o	  The effective user ID of the process matches the user ID  of
		  the  owner of the file and the appropriate access bit of the
		  "owner" portion (0700) of the file mode is set.

	   o	  The effective user  ID of the process	 does  not  match  the
		  user	ID  of the owner of the file, but either the effective
		  group ID or one of  the  supplementary  group	  IDs  of  the
		  process  match the group  ID of the file and the appropriate
		  access bit of the "group" portion (0070) of the file mode is
		  set.

	   o	  The effective user ID of the process does not match the user
		  ID of the owner of the file, and neither the effective group
		  ID  nor  any	of  the supplementary group IDs of the process
		  match the group ID of the file, but the  appropriate	access
		  bit of the "other" portion (0007) of the file mode is set.

	   o	  The  read,  write,  or  execute  mode bit is not set but the
		  process has the discretionary file access override privilege
		  for the corresponding mode bit: {PRIV_FILE_DAC_READ} for the
		  read	bit   {PRIV_FILE_DAC_WRITE}   for   the	  write	  bit,
		  {PRIV_FILE_DAC_SEARCH}  for  the execute bit on directories,
		  and {PRIV_FILE_DAC_EXECUTE} for the executable bit on	 plain
		  files.

       Otherwise, the corresponding permissions are denied.

   File Descriptor
       A file descriptor is a small integer used to perform I/O on a file. The
       value of a file descriptor is from 0 to (NOFILES−1). A process may have
       no  more	 than	NOFILES	 file descriptors  open simultaneously. A file
       descriptor is returned by calls such as open(2) or  pipe(2).  The  file
       descriptor  is  used as an argument by calls such as read(2), write(2),
       ioctl(2), and close(2).

       Each file descriptor has a corresponding offset	maximum.  For  regular
       files that were opened without setting the O_LARGEFILE flag, the offset
       maximum is 2 Gbyte − 1 byte (2^31 −1 bytes).  For  regular  files  that
       were  opened  with the O_LARGEFILE flag set, the offset maximum is 2^63
       −1 bytes.

   File Name
       Names consisting of 1 to	 NAME_MAX characters may be used  to  name  an
       ordinary file, special file or directory.

       These  characters  may be selected from the set of all character values
       excluding \0 (null) and the ASCII code for / (slash).

       Note that it is generally unwise to use *, ?, [, or ] as part  of  file
       names  because  of  the special meaning attached to these characters by
       the shell (see sh(1), csh(1), and ksh(1)). Although permitted, the  use
       of unprintable characters in file names should be avoided.

       A  file	name  is  sometimes  referred to as a pathname component.  The
       interpretation of a pathname component is dependent on  the  values  of
       NAME_MAX	 and   _POSIX_NO_TRUNC associated with the path prefix of that
       component.  If any pathname  component  is  longer  than	 NAME_MAX  and
       _POSIX_NO_TRUNC is in effect for the path prefix of that component (see
       fpathconf(2) and limits.h(3HEAD)), it shall be considered an error con‐
       dition in  that implementation. Otherwise, the implementation shall use
       the first NAME_MAX bytes of the pathname component.

   Foreground Process Group
       Each session that has established a connection with a controlling  ter‐
       minal  will  distinguish	 one process group of the session as the fore‐
       ground process group of the controlling terminal.  This group has  cer‐
       tain privileges when accessing its controlling terminal that are denied
       to background process groups.

   {IOV_MAX}
       Maximum number of entries in a struct iovec array.

   {LIMIT}
       The braces notation, {LIMIT}, is used to denote a magnitude  limitation
       imposed	by  the	 implementation.  This	indicates a value which may be
       defined by a header file (without the braces), or the actual value  may
       be  obtained  at	 runtime  by a call to the configuration inquiry path‐
       conf(2) with the name argument  _PC_LIMIT.

   Masks
       The file mode creation mask of the process used during any create func‐
       tion  calls  to turn off permission bits in the mode argument supplied.
       Bit positions that are set in umask(cmask) are cleared in the  mode  of
       the created file.

   Message
       In a stream, one or more blocks of data or information, with associated
       STREAMS control structures. Messages can be of several  defined	types,
       which  identify	the  message  contents. Messages are the only means of
       transferring data and communicating within a stream.

   Message Queue
       In a stream, a linked list of messages awaiting processing by a	module
       or driver.

   Message Queue Identifier
       A message queue identifier (msqid) is a unique positive integer created
       by a msgget(2) call. Each msqid has a message queue and a  data	struc‐
       ture  associated with it. The data structure is referred to as msqid_ds
       and contains the following members:

	 struct	    ipc_perm msg_perm;
	 struct	    msg *msg_first;
	 struct	    msg *msg_last;
	 ulong_t    msg_cbytes;
	 ulong_t    msg_qnum;
	 ulong_t    msg_qbytes;
	 pid_t	    msg_lspid;
	 pid_t	    msg_lrpid;
	 time_t	    msg_stime;
	 time_t	    msg_rtime;
	 time_t	    msg_ctime;

       The following are descriptions of the msqid_ds structure members:

       The msg_perm member is an ipc_perm structure that specifies the message
       operation permission (see below). This structure includes the following
       members:

	 uid_t	  cuid;	  /* creator user id */
	 gid_t	  cgid;	  /* creator group id */
	 uid_t	  uid;	  /* user id */
	 gid_t	  gid;	  /* group id */
	 mode_t	  mode;	  /* r/w permission */
	 ulong_t  seq;	  /* slot usage sequence # */
	 key_t	  key;	  /* key */

       The *msg_first member is a pointer to the first message on the queue.

       The *msg_last member is a pointer to the last message on the queue.

       The msg_cbytes member is the current number of bytes on the queue.

       The msg_qnum member is the number of messages currently on the queue.

       The msg_qbytes member is the maximum number of  bytes  allowed  on  the
       queue.

       The  msg_lspid  member  is the process ID of the last process that per‐
       formed a msgsnd() operation.

       The msg_lrpid member is the process id of the last  process  that  per‐
       formed a msgrcv() operation.

       The msg_stime member is the time of the last msgsnd() operation.

       The msg_rtime member is the time of the last msgrcv() operation.

       The  msg_ctime  member  is the time of the last msgctl() operation that
       changed a member of the above structure.

   Message Operation Permissions
       In the msgctl(2), msgget(2), msgrcv(2), and msgsnd(2) function descrip‐
       tions,  the  permission	required for an operation is given as {token},
       where token is the type of permission needed, interpreted as follows:

	 00400	 READ by user
	 00200	 WRITE by user
	 00040	 READ by group
	 00020	 WRITE by group
	 00004	 READ by others
	 00002	 WRITE by others

       Read and write permissions for a msqid are granted to a process if  one
       or more of the following are true:

	   o	  The {PRIV_IPC_DAC_READ} or {PRIV_IPC_DAC_WRITE} privilege is
		  present in the effective set.

	   o	  The effective user ID of the process	matches	 msg_perm.cuid
		  or  msg_perm.uid in the data structure associated with msqid
		  and the appropriate bit of  the  "user"  portion  (0600)  of
		  msg_perm.mode is set.

	   o	  Any  group  ID  in  the  process  credentials	 from  the set
		  (cr_gid, cr_groups) matches  msg_perm.cgid  or  msg_perm.gid
		  and  the  appropriate	 bit  of  the "group" portion (060) of
		  msg_perm.mode is set.

	   o	  The  appropriate  bit	 of  the  "other"  portion  (006)   of
		  msg_perm.mode is set."

       Otherwise, the corresponding permissions are denied.

   Module
       A module is an entity containing processing routines for input and out‐
       put data. It always exists in the  middle  of  a	 stream,  between  the
       stream's	 head and a driver. A module is the STREAMS counterpart to the
       commands in a shell pipeline except that a module contains  a  pair  of
       functions   which   allow  independent  bidirectional  (downstream  and
       upstream) data flow and processing.

   Multiplexor
       A multiplexor is a driver that allows streams associated	 with  several
       user  processes	to be connected to a single driver, or several drivers
       to be connected to a single user process. STREAMS does  not  provide  a
       general	multiplexing  driver, but does provide the facilities for con‐
       structing  them	and  for  connecting  multiplexed  configurations   of
       streams.

   Offset Maximum
       An  offset  maximum  is an attribute of an open file description repre‐
       senting the largest value that can be used as a file offset.

   Orphaned Process Group
       A process group in which the parent of every member  in	the  group  is
       either  itself a member of the group, or is not a member of the process
       group's session.

   Path Name
       A path name is a null-terminated	 character  string  starting  with  an
       optional	 slash (/), followed by zero or more directory names separated
       by slashes, optionally followed by a file name.

       If a path name begins with a slash, the path search begins at the  root
       directory. Otherwise, the search begins from the current working direc‐
       tory.

       A slash by itself names the root directory.

       Unless specifically stated otherwise, the null path name is treated  as
       if it named a non-existent file.

   Privileged User
       Solaris	software  implements  a	 set  of privileges that provide fine-
       grained control over the actions of processes. The possession of	 of  a
       certain	privilege  allows  a  process  to  perform  a  specific set of
       restricted operations. Prior to the Solaris 10 release, a process  run‐
       ning  with  uid 0 was granted all privileges. See privileges(5) for the
       semantics and the degree of backward compatibility awarded to processes
       with an effective uid of 0.

   Process ID
       Each  process  in the system is uniquely identified during its lifetime
       by a positive integer called a process  ID.  A  process	ID  cannot  be
       reused  by  the	system until the process lifetime, process group life‐
       time, and session lifetime ends for any process ID, process  group  ID,
       and  session  ID	 equal	to that process ID. There are threads within a
       process with thread IDs thread_t and LWPID_t.  These  threads  are  not
       visible to the outside process.

   Parent Process ID
       A  new  process is created by a currently active process (see fork(2)).
       The parent process ID of a process is the process ID of its creator.

   Privilege
       Having appropriate privilege means having the  capability  to  override
       system restrictions.

   Process Group
       Each process in the system is a member of a process group that is iden‐
       tified by a process group ID.  Any process that is not a process	 group
       leader  may  create  a  new  process  group  and become its leader. Any
       process that is not  a  process	group  leader  may  join  an  existing
       process	group  that  shares  the same session as the process.  A newly
       created process joins the process group of its parent.

   Process Group Leader
       A process group leader is a process whose process ID is the same as its
       process group ID.

   Process Group ID
       Each active process is a member of a process group and is identified by
       a positive integer called the process group ID. This ID is the  process
       ID  of the group leader. This grouping permits the signaling of related
       processes (see kill(2)).

   Process Lifetime
       A process lifetime begins when the process is forked and ends after  it
       exits,  when  its  termination  has  been  acknowledged	by  its parent
       process. See wait(3C).

   Process Group Lifetime
       A process group lifetime begins when the process group  is  created  by
       its  process  group  leader,  and  ends	when  the lifetime of the last
       process in the group ends or when the last process in the group	leaves
       the group.

   Processor Set ID
       The  processors	in a system may be divided into subsets, known as pro‐
       cessor sets. A process bound to one of these sets will run only on pro‐
       cessors	in  that  set, and the processors in the set will normally run
       only processes that have been bound to the set. Each  active  processor
       set is identified by a positive integer. See pset_create(2).

   Read Queue
       In  a  stream,  the message queue in a module or driver containing mes‐
       sages moving upstream.

   Real User ID and Real Group ID
       Each user allowed on the system is  identified by a positive integer (0
       to  MAXUID) called a real user ID.

       Each  user  is  also  a member of a group. The group is identified by a
       positive integer called the real group ID.

       An active process has a real user ID and real group ID that are set  to
       the real user ID and real group ID, respectively, of the user responsi‐
       ble for the creation of the process.

   Root Directory and Current Working Directory
       Each process has associated with it a concept of a root directory and a
       current	working	 directory  for	 the  purpose  of  resolving path name
       searches. The root directory of a process need not be the  root	direc‐
       tory of the root file system.

   Saved Resource Limits
       Saved  resource	limits is an attribute of a process that provides some
       flexibility in the handling  of	unrepresentable	 resource  limits,  as
       described in the exec family of functions and setrlimit(2).

   Saved User ID and Saved Group ID
       The  saved  user ID and saved group ID are the values of the  effective
       user ID and effective group ID just after an exec of a file  whose  set
       user or set group file mode bit has been set (see exec(2)).

   Semaphore Identifier
       A semaphore identifier (semid) is a unique positive  integer created by
       a semget(2) call. Each semid has a set of semaphores and a data	struc‐
       ture  associated with it. The data structure is referred to as semid_ds
       and contains the following members:

	 struct ipc_perm   sem_perm;	/* operation permission struct */
	 struct sem	   *sem_base;	/* ptr to first semaphore in set */
	 ushort_t	   sem_nsems;	/* number of sems in set */
	 time_t		   sem_otime;	/* last operation time */
	 time_t		   sem_ctime;	/* last change time */
					/* Times measured in secs since */
					/* 00:00:00 GMT, Jan. 1, 1970 */

       The following are descriptions of the semid_ds structure members:

       The sem_perm member is an ipc_perm structure that specifies  the	 sema‐
       phore  operation	 permission  (see  below). This structure includes the
       following members:

	 uid_t	   uid;	   /* user id */
	 gid_t	   gid;	   /* group id */
	 uid_t	   cuid;   /* creator user id */
	 gid_t	   cgid;   /* creator group id */
	 mode_t	   mode;   /* r/a permission */
	 ulong_t   seq;	   /* slot usage sequence number */
	 key_t	   key;	   /* key */

       The sem_nsems member is equal to the number of semaphores in  the  set.
       Each  semaphore	in  the	 set  is  referenced  by a nonnegative integer
       referred to as a sem_num. sem_num values run sequentially from 0 to the
       value of sem_nsems minus 1.

       The sem_otime member is the time of the last semop(2) operation.

       The  sem_ctime  member is the time of the last semctl(2) operation that
       changed a member of the above structure.

       A semaphore is a data structure called sem that contains the  following
       members:

	 ushort_t   semval;    /* semaphore value */
	 pid_t	    sempid;    /* pid of last operation	 */
	 ushort_t   semncnt;   /* # awaiting semval > cval */
	 ushort_t   semzcnt;   /* # awaiting semval = 0 */

       The following are descriptions of the sem structure members:

       The semval member is a non-negative integer that is the actual value of
       the semaphore.

       The sempid member is equal to the process ID of the last	 process  that
       performed a semaphore operation on this semaphore.

       The  semncnt member is a count of the number of processes that are cur‐
       rently suspended awaiting this semaphore's  semval  to  become  greater
       than its current value.

       The  semzcnt member is a count of the number of processes that are cur‐
       rently suspended awaiting this semaphore's semval to become 0.

   Semaphore Operation Permissions
       In the semop(2) and semctl(2)  function	descriptions,  the  permission
       required	 for an operation is given as {token}, where token is the type
       of permission needed interpreted as follows:

	 00400	     READ by user
	 00200	 ALTER by user
	 00040	 READ by group
	 00020	 ALTER by group
	 00004	 READ by others
	 00002	 ALTER by others

       Read and alter permissions for a semid are granted to a process if  one
       or more of the following are true:

	   o	  The {PRIV_IPC_DAC_READ} or {PRIV_IPC_DAC_WRITE} privilege is
		  present in the effective set.

	   o	  The effective user ID of the process	matches	 sem_perm.cuid
		  or  sem_perm.uid in the data structure associated with semid
		  and the appropriate bit of  the  "user"  portion  (0600)  of
		  sem_perm.mode is set.

	   o	  The  effective group ID of the process matches sem_perm.cgid
		  or sem_perm.gid and the appropriate bit of the "group"  por‐
		  tion (060) of sem_perm.mode is set.

	   o	  The	appropriate   bit  of  the  "other"  portion  (06)  of
		  sem_perm.mode is set.

       Otherwise, the corresponding permissions are denied.

   Session
       A session is a group of processes identified by a common	 ID  called  a
       session	 ID,  capable  of establishing a connection with a controlling
       terminal.   Any process that is not a process group leader may create a
       new session  and process group, becoming the session leader of the ses‐
       sion and process group leader of the process group.   A	newly  created
       process joins the session of its creator.

   Session ID
       Each  session  in the system is uniquely identified during its lifetime
       by  a positive integer called a session ID, the process ID of its  ses‐
       sion leader.

   Session Leader
       A  session  leader  is  a  process  whose session ID is the same as its
       process and process group ID.

   Session Lifetime
       A session lifetime begins when the session is created  by  its  session
       leader, and ends when the lifetime of the last process that is a member
       of the session ends, or when the last process that is a member  in  the
       session leaves the session.

   Shared Memory Identifier
       A shared memory identifier (shmid) is a unique positive integer created
       by a shmget(2) call. Each shmid has a segment of memory (referred to as
       a shared memory segment) and a data structure associated with it. (Note
       that these shared memory segments must be  explicitly  removed  by  the
       user  after  the last reference to them is removed.) The data structure
       is referred to as shmid_ds and contains the following members:

	 struct ipc_perm   shm_perm;	 /* operation permission struct */
	 size_t		   shm_segsz;	 /* size of segment */
	 struct anon_map   *shm_amp;	 /* ptr to region structure */
	 char		   pad[4];	 /* for swap compatibility */
	 pid_t		   shm_lpid;	 /* pid of last operation */
	 pid_t		   shm_cpid;	 /* creator pid */
	 shmatt_t	   shm_nattch;	 /* number of current attaches */
	 ulong_t	   shm_cnattch;	 /* used only for shminfo */
	 time_t		   shm_atime;	 /* last attach time */
	 time_t		   shm_dtime;	 /* last detach time */
	 time_t		   shm_ctime;	 /* last change time */
					 /* Times measured in secs since */
					 /* 00:00:00 GMT, Jan. 1, 1970 */

       The following are descriptions of the shmid_ds structure members:

       The shm_perm member is an ipc_perm structure that specifies the	shared
       memory  operation  permission  (see below). This structure includes the
       following members:

	 uid_t	   cuid;   /* creator user id */
	 gid_t	   cgid;   /* creator group id */
	 uid_t	   uid;	   /* user id */
	 gid_t	   gid;	   /* group id */
	 mode_t	   mode;   /* r/w permission */
	 ulong_t   seq;	   /* slot usage sequence # */
	 key_t	   key;	   /* key */

       The shm_segsz member specifies the size of the shared memory segment in
       bytes.

       The  shm_cpid  member is the process ID of the process that created the
       shared memory identifier.

       The shm_lpid member is the process ID of the  last  process  that  per‐
       formed a shmat() or shmdt() operation (see shmop(2)).

       The  shm_nattch	member	is the number of processes that currently have
       this segment attached.

       The shm_atime member is the time of the	last  shmat()  operation  (see
       shmop(2)).

       The  shm_dtime  member  is  the time of the last shmdt() operation (see
       shmop(2)).

       The shm_ctime member is the time of the last shmctl(2)  operation  that
       changed one of the members of the above structure.

   Shared Memory Operation Permissions
       In the shmctl(2), shmat(), and shmdt() (see shmop(2)) function descrip‐
       tions, the permission required for an operation is  given  as  {token},
       where token is the type of permission needed interpreted as follows:

	 00400	 READ by user
	 00200	 WRITE by user
	 00040	 READ by group
	 00020	 WRITE by group
	 00004	 READ by others
	 00002	 WRITE by others

       Read  and write permissions for a shmid are granted to a process if one
       or more of the following are true:

	   o	  The {PRIV_IPC_DAC_READ} or {PRIV_IPC_DAC_WRITE} privilege is
		  present in the effective set.

	   o	  The  effective  user ID of the process matches shm_perm.cuid
		  or shm_perm.uid in the data structure associated with	 shmid
		  and  the  appropriate	 bit  of  the "user" portion (0600) of
		  shm_perm.mode is set.

	   o	  The effective group ID of the process matches	 shm_perm.cgid
		  or  shm_perm.gid and the appropriate bit of the "group" por‐
		  tion (060) of shm_perm.mode is set.

	   o	  The  appropriate  bit	 of  the  "other"  portion   (06)   of
		  shm_perm.mode is set.

       Otherwise, the corresponding permissions are denied.

   Special Processes
       The  process  with ID 0 and the process with ID 1 are special processes
       referred to as proc0 and proc1;	see  kill(2).  proc0  is  the  process
       scheduler.  proc1  is  the  initialization process (init); proc1 is the
       ancestor of every other process in the system and is  used  to  control
       the process structure.

   STREAMS
       A set of kernel mechanisms that support the development of network ser‐
       vices and data communication drivers. It	 defines  interface  standards
       for character input/output within the kernel and between the kernel and
       user level processes. The STREAMS mechanism is composed of utility rou‐
       tines, kernel facilities and a set of data structures.

   Stream
       A  stream  is a full-duplex data path within the kernel	between a user
       process and driver routines. The primary components are a stream	 head,
       a  driver, and zero or more modules between the stream head and driver.
       A stream is analogous to a shell pipeline, except that  data  flow  and
       processing are bidirectional.

   Stream Head
       In a stream, the stream head is the end of the stream that provides the
       interface between the stream and a user process.	 The  principal	 func‐
       tions  of  the  stream head are processing STREAMS-related system calls
       and passing data and information between a user process and the stream.

   Upstream
       In a stream, the direction from driver to stream head.

   Write Queue
       In a stream, the message queue in a module or  driver  containing  mes‐
       sages moving downstream.

ACKNOWLEDGMENTS
       Sun  Microsystems, Inc. gratefully acknowledges The Open Group for per‐
       mission to reproduce portions of its copyrighted documentation.	Origi‐
       nal  documentation  from	 The  Open  Group  can	be  obtained online at
       http://www.opengroup.org/bookstore/.

       The Institute of Electrical and	Electronics  Engineers	and  The  Open
       Group, have given us permission to reprint portions of their documenta‐
       tion.

       In the following statement, the phrase ``this text'' refers to portions
       of the system documentation.

       Portions	 of  this text are reprinted and reproduced in electronic form
       in the SunOS Reference Manual, from  IEEE  Std  1003.1,	2004  Edition,
       Standard for Information Technology -- Portable Operating System Inter‐
       face (POSIX), The Open Group Base Specifications Issue 6, Copyright (C)
       2001-2004 by the Institute of Electrical and Electronics Engineers, Inc
       and The Open Group.  In the event of any discrepancy between these ver‐
       sions  and  the original IEEE and The Open Group Standard, the original
       IEEE and The Open Group Standard is the referee document.  The original
       Standard	    can	    be	  obtained    online	at    http://www.open‐
       group.org/unix/online.html.

       This notice shall appear on any product containing this material.

SEE ALSO
       standards(5), threads(5)

SunOS 5.11			  17 Nov 2008			      Intro(2)
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