Return to intro.2 CVS log

Up to [Power 6/32 Unix Tahoe 4.2BSD] / cci / usr / src / man / man2

Power 6/32 Unix version 1.2b

.TH INTRO 2
.de {n
.HP
\\$1  \\$2  \\$3
.br
..
.SH NAME
intro \- introduction to system calls and error numbers
.SH SYNOPSIS
.B #include \|<errno.h>
.SH DESCRIPTION
This section
describes all of the system calls.
Most of these calls have one or more error returns.
An error condition is indicated by an otherwise
impossible returned value.
This is almost always \-1;
the individual descriptions specify the details.
An error number is also made available
in the external variable
.IR errno .
.I Errno\^
is not cleared on successful calls, so it should be tested only
after an error has been indicated.
.PP
Each system call description attempts to
list all possible error numbers.
The following is a complete list of the error numbers and
their names as defined in
.BR <errno.h> .
.{n 1 \s-1EPERM\s+1 "Not owner"
Typically this error indicates
an attempt to modify a file in some way forbidden
except to its owner or super-user.
It is also returned for attempts
by ordinary users to do things
allowed only to the super-user.
.{n 2 \s-1ENOENT\s+1 "No such file or directory"
This error occurs when a file name is specified
and the file should exist but doesn't, or when one
of the directories in a path name does not exist.
.{n 3 \s-1ESRCH\s+1 "No such process"
No process can be found corresponding to that specified by
.I pid\^
in
.I kill\^
or
.IR ptrace .
.{n 4 \s-1EINTR\s+1 "Interrupted system call"
An asynchronous signal (such as interrupt or quit),
which the user has elected to catch,
occurred during a system call.
If execution is resumed
after processing the signal,
it will appear as if the interrupted system call
returned this error condition.
.{n 5 \s-1EIO\s+1 "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.
.{n 6 \s-1ENXIO\s+1 "No such device or address"
I/O on a special file refers to a subdevice which does not
exist,
or beyond the limits of the device.
It may also occur when, for example, a tape drive
is not on-line or no disk pack is loaded on a drive.
.{n 7 \s-1E2BIG\s+1 "Arg list too long"
An argument list longer than 5,120 bytes
is presented to a member of the
.I exec\^
family.
.{n 8 \s-1ENOEXEC\s+1 "Exec format error"
A request is made to execute a file
which, although it has the appropriate permissions,
does not start with a valid magic number (see
.IR a.out (4)).
.{n 9 \s-1EBADF\s+1 "Bad file number"
Either a file descriptor refers to no
open file,
or a read (respectively, write) request is made to
a file which is open only for writing (respectively, reading).
.{n 10 \s-1ECHILD\s+1 "No child processes"
A
.I wait
was executed by a process that had no existing or unwaited-for child processes.
.{n 11 \s-1EAGAIN\s+1 "No more processes"
A
.I fork
failed because the system's process table is full
or the user is not allowed to create any more
processes.
.{n 12 \s-1ENOMEM\s+1 "Not enough space"
During an
.IR exec ,
.IR brk ,
or
.IR sbrk ,
a program asks for more space than the system is able to supply.
This is not a temporary condition; the maximum space size
is a system parameter.
The error may also occur if the arrangement
of text, data, and stack segments
requires too many segmentation registers, or
if there is not enough swap space during a
.IR fork .
.{n 13 \s-1EACCES\s+1 "Permission denied"
An attempt was made to access a file in a way forbidden
by the protection system.
.{n 14 \s-1EFAULT\s+1 "Bad address"
The system encountered a hardware fault in attempting to
use an argument of a system call.
.{n 15 \s-1ENOTBLK\s+1 "Block device required"
A non-block file was mentioned where a block device was required,
e.g., in
.IR mount .
.{n 16 \s-1EBUSY\s+1 "Device or resource busy"
An attempt was made to mount a device that was already mounted or
an attempt was made to dismount 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.
.{n 17 \s-1EEXIST\s+1 "File exists"
An existing file was mentioned in an inappropriate context,
e.g.,
.IR link .
.{n 18 \s-1EXDEV\s+1 "Cross-device link"
A link to a file on another device
was attempted.
.{n 19 \s-1ENODEV\s+1 "No such device"
An attempt was made to apply an inappropriate
system call to a device;
e.g., read a write-only device.
.{n 20 \s-1ENOTDIR\s+1 "Not a directory"
A non-directory was specified where a directory
is required,
for example in a path prefix or
as an argument to
.IR chdir (2).
.{n 21 \s-1EISDIR\s+1 "Is a directory"
An attempt was made to write on a directory.
.{n 22 \s-1EINVAL\s+1 "Invalid argument"
Some invalid argument (e.g., dismounting a non-mounted device;
mentioning an undefined signal in
.IR signal ,
or
.IR kill ;
reading or writing a file for which
.I lseek\^
has generated a negative pointer).
Also set by the math functions described in the (3M) entries
of this manual.
.{n 23 \s-1ENFILE\s+1 "File table overflow"
The system file table is full,
and temporarily no more
.I opens\^
can be accepted.
.{n 24 \s-1EMFILE\s+1 "Too many open files"
No process may have more than 20 file descriptors open at a time.
.{n 25 \s-1ENOTTY\s+1 "Not a character device"
An attempt was made to \f2ioctl\fR(2) a file that
is not a special character device.
.{n 26 \s-1ETXTBSY\s+1 "Text file busy"
An attempt was made to execute a pure-procedure
program that is currently open for writing.
Also an attempt to open for writing a pure-procedure
program that is being executed.
.{n 27 \s-1EFBIG\s+1 "File too large"
The size of a file exceeded the maximum
file size (1,082,201,088 bytes) or
.SM ULIMIT\*S;
see
.IR ulimit (2).
.{n 28 \s-1ENOSPC\s+1 "No space left on device"
During a
.I write\^
to an ordinary file,
there is no free space left on the device.
.{n 29 \s-1ESPIPE\s+1 "Illegal seek"
An
.I lseek\^
was issued to a pipe.
.{n 30 \s-1EROFS\s+1 "Read-only file system"
An attempt to modify a file or directory
was made
on a device mounted read-only.
.{n 31 \s-1EMLINK\s+1 "Too many links"
An attempt to make more than the maximum number of links (1000) to a file.
.{n 32 \s-1EPIPE\s+1 "Broken pipe"
A write on a pipe for which there is no process
to read the data.
This condition normally generates a signal;
the error is returned if the signal is ignored.
.{n 33 \s-1EDOM\s+1 "Math argument"
The argument of a function in the math package (3M)
is out of the domain of the function.
.{n 34 \s-1ERANGE\s+1 "Result too large"
The value of a function in the math package (3M)
is not representable within machine precision.
.{n 35 \s-1EWOULDBLOCK\s+1 "Operation would block"
An operation which would cause a process to block was attempted
on a object in non-blocking mode (see \fIioctl\fP (2)).
.{n 36 \s-1EINPROGRESS\s+1 "Operation now in progress"
An operation which takes a long time to complete (such as
a \fIconnect\fP (2)) was attempted on a non-blocking object (see
\fIioctl\fP (2)).
.{n 37 \s-1EALREADY\s+1 "Operation already in progress"
An operation was attempted on a non-blocking object which already
had an operation in progress.
.{n 38 \s-1ENOTSOCK\s+1 "Socket operation on non-socket"
Self-explanatory.
.{n 39 \s-1EDESTADDRREQ\s+1 "Destination address required"
A required address was omitted from an operation on a socket.
.{n 40 \s-1EMSGSIZE\s+1 "Message too long"
A message sent on a socket was larger than the internal message buffer.
.{n 41 \s-1EPROTOTYPE\s+1 "Protocol wrong type for socket"
A protocol was specified which does not support the semantics of the
socket type requested. For example you cannot use the ARPA Internet
UDP protocol with type SOCK_STREAM.
.{n 42 \s-1ENOPROTOOPT\s+1 "Bad protocol option"
A bad option was specified in a
.IR getsockopt (2)
or
.IR setsockopt (2)
call.
.{n 43 \s-1EPROTONOSUPPORT\s+1 "Protocol not supported"
The protocol has not been configured into the
system or no implementation for it exists.
.{n 44 \s-1ESOCKTNOSUPPORT\s+1 "Socket type not supported"
The support for the socket type has not been configured into the
system or no implementation for it exists.
.{n 45 \s-1EOPNOTSUPP\s+1 "Operation not supported on socket"
For example, trying to \fIaccept\fP a connection on a datagram socket.
.{n 46 \s-1EPFNOSUPPORT\s+1 "Protocol family not supported"
The protocol family has not been configured into the
system or no implementation for it exists.
.{n 47 \s-1EAFNOSUPPORT\s+1 "Address family not supported by protocol family"
An address incompatible with the requested protocol was used.
For example, you shouldn't necessarily expect to be able to use PUP
Internet addresses with ARPA Internet protocols.
.{n 48 \s-1EADDRINUSE\s+1 "Address already in use"
Only one usage of each address is normally permitted.
.{n 49 \s-1EADDRNOTAVAIL\s+1 "Can't assign requested address"
Normally results from an attempt to create a socket with an
address not on this machine.
.{n 50 \s-1ENETDOWN\s+1 "Network is down"
A socket operation encountered a dead network.
.{n 51 \s-1ENETUNREACH\s+1 "Network is unreachable"
A socket operation was attempted to an unreachable network.
.{n 52 \s-1ENETRESET\s+1 "Network dropped connection on reset"
The host you were connected to crashed and rebooted.
.{n 53 \s-1ECONNABORTED\s+1 "Software caused connection abort"
A connection abort was caused internal to your host machine.
.{n 54 \s-1ECONNRESET\s+1 "Connection reset by peer"
A connection was forcibly closed by a peer.  This normally
results from the peer executing a \fIshutdown\fP (2) call.
.{n 55 \s-1ENOBUFS\s+1 "No buffer space available"
An operation on a socket or pipe was not performed because
the system lacked sufficient buffer space.
.{n 56 \s-1EISCONN\s+1 "Socket is already connected"
A
.I connect
request was made on an already connected socket; or,
a
.I sendto
or
.I sendmsg
request on a connected socket specified a destination
other than the connected party.
.{n 57 \s-1ENOTCONN\s+1 "Socket is not connected"
An request to send or receive data was disallowed because
the socket is not connected.
.{n 58 \s-1ESHUTDOWN\s+1 "Can't send after socket shutdown"
A request to send data was disallowed because the socket
had already been shut down with a previous
.IR shutdown (2)
call.
.{n 59 \fIunused\fP
.{n 60 \s-1ETIMEDOUT\s+1 "Connection timed out"
A
.I connect
request failed because the connected party did not
properly respond after a period of time.  (The timeout
period is dependent on the communication protocol.)
.{n 61 \s-1ECONNREFUSED\s+1 "Connection refused"
No connection could be made because the target machine actively
refused it.  This usually results from trying to connect
to a service which is inactive on the foreign host.
.{n 62 \s-1ELOOP\s+1 "Too many levels of symbolic links"
A path name lookup involved more than 8 symbolic links.
.{n 63 \s-1ENAMETOOLONG\s+1 "File name too long"
A component of a path name exceeded 255 characters, or an entire
path name exceeded 1023 characters.
.{n 64 \s-1EHOSTDOWN\s+1 "Host is down"
The host machine is not up.
.{n 65 \s-1EHOSTUNREACH\s+1 "No route to host"
The host machine cannot be reached.
.{n 66 \s-1ENOTEMPTY\s+1 "Directory not empty"
A directory with entries other than \*(lq.\*(rq and \*(lq..\*(rq
was supplied to a remove directory or rename call.
.{n 67 \fIunused\fP
.{n 68 \s-1EUSERS\s+1 "Too many users"
The quota table is full.
.{n 69 \s-1EDQUOT\s+1 "Disc quota exceeded"
A process has exceeded its disk quota.
.{n 70 \s-1ENOMSG\s+1 "No message of desired type"
An attempt was made to receive a message of a type
that does not exist on the specified message queue; see
.IR msgop (2).
.{n 71 \s-1EIDRM\s+1 "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
.IR msgctl "(2), " semctl "(2), and " shmctl (2)).
.SH "DEFINITIONS"
.SS "Process \s-1ID\s+1"
Each active process in the system is uniquely identified by a
positive integer called a process
.SM ID\*S.
The range of this
.SM ID
is from 1 to 30,000.
.SS "Parent Process \s-1ID\s+1"
A new process is created by a currently active
process; see
.IR fork (2).
The parent process
.SM ID
of a process is the process
.SM ID
of its creator.
.SS "Process Group \s-1ID\s+1"
Each active process is a member of a process group that is
identified by a positive integer called the process group
.SM ID\*S.
This
.SM ID
is the process
.SM ID
of the group leader.
This grouping permits the signaling of related processes; see
.IR kill (2).
.SS "Tty Group \s-1ID\s+1"
Each active process can be a member of a terminal group that
is identified by a positive integer called the tty group
.SM ID\*S.
This grouping is used to terminate a group of related processes upon termination
of one of the processes in the group; see
.IR exit (2)
and
.IR signal (2).
.SS "Real User \s-1ID\s+1 and Real Group \s-1ID\s+1"
Each user allowed on the system is 
identified by a positive integer called a real user
.SM ID\*S.
.PP
Each user is also a member of a group.
The group is identified by a positive integer called the real group
.SM ID\*S.
.PP
An active process has a real user
.SM ID
and real group
.SM ID
that are set to the real user
.SM ID
and real group
.SM ID\*S,
respectively, of the user responsible for the creation of the process.
.SS "Effective User \s-1ID\s+1 and Effective Group \s-1ID\s+1"
An active process has an effective user
.SM ID
and an effective group
.SM ID
that are used to determine file access permissions (see below).
The effective
user
.SM ID
and effective group
.SM ID
are equal to the process's real user
.SM ID
and real group
.SM ID
respectively, unless the process
or one of its ancestors evolved from a file that had the set-user-\s-1ID\s+1
bit or set-group
.SM ID
bit set; see
.IR exec (2).
.SS Super-user
A process is recognized as a
.I super-user\^
process and is granted special privileges if its effective user
.SM ID
is 0.
.SS "Special Processes"
The processes with a process
.SM ID
of 0 and a process
.SM ID
of 1 are special processes and are referred to as
.IR proc0 " and " proc1.
.PP
.I Proc0\^
is the scheduler.
.I Proc1\^
is the initialization process 
.RI ( init ).
Proc1 is the ancestor of every other
process in the system and is used to control the process structure.
.SS File Descriptor
A file descriptor is a small integer used
to do \s-1I/O\s+1 on a file.
The value of a file descriptor is from
0 to 19.
A process may have no more than 20 file descriptors (0-19)
open simultaneously.
A file descriptor is returned by system calls such as
\f2open\fR(2),
or \f2pipe\fR(2).
The file descriptor is used as an
argument by calls such as
\f2read\fR(2),
\f2write\fR(2),
\f2ioctl\fR(2),
and
\f2close\fR(2).
.SS "File Name"
Names consisting of 1 to 14 characters may be used to name an ordinary file,
special file or directory.
.PP
These characters may be selected from the set of all character values
excluding \e0 (null) and the
.SM ASCII
code for
.B /
(slash).
.PP
Note that it is generally unwise to use
.BR "*" ,
.BR "?" ,
.BR "[" ,
or
.B "]"
as part of file names because of the special meaning attached to these
characters by the shell.
See
.IR sh (1).
Although permitted, it is advisable to avoid the use of unprintable
characters in file names.
.SS "Path Name and Path Prefix"
A path name is a null-terminated character string
starting with an optional slash
.RB ( / ),
followed by
zero or more directory names separated by slashes, optionally followed
by a file name.
.PP
More precisely, a path name is a null-terminated character string
constructed as follows:
.PP
.RS
<path-name>::=<file-name>\(bv<path-prefix><file-name>|/
.br
<path-prefix>::=<rtprefix>\(bv/<rtprefix>
.br
<rtprefix>::=<dirname>/\(bv<rtprefix><dirname>/
.RE
.PP
where <file-name> is a string of 1 to 14
characters other than the
.SM ASCII
slash and null, and
<dirname> is a string of 1 to 14 characters
(other than the
.SM ASCII
slash and null)
that names a directory.
.PP
If a path name begins with a slash, the path search begins at the
.I root\^
directory.
Otherwise, the search begins from the current working directory.
.PP
A slash by itself names the root directory.
.PP
Unless specifically stated otherwise,
the null path name is treated as if it named
a non-existent file.
.SS Directory
.PP
Directory entries are called links.
By convention, a directory contains at least two links,
.B  .
and
.BR .. ,
referred to as
.I dot\^
and
.I dot-dot\^
respectively.
Dot refers to the directory itself and dot-dot refers to its parent
directory.
.SS "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 directory of the root
file system.
.SS "File Access Permissions"
.PP
Read, write, and execute/search permissions on a file are
granted to a process if one or more of the following are true:
.IP
The effective user
.SM ID
of the process
is super-user.
.IP
The effective user
.SM ID
of the process
matches the user
.SM ID
of the owner of the file
and the appropriate access bit of the
``owner'' portion (0700) of the file mode is set.
.IP
The effective user
.SM ID
of the process
does not match the user
.SM ID
of the owner of the file,
and the effective group
.SM ID
of the process
matches the group of the file and
the appropriate access bit of the ``group'' portion
(070) of the file mode is set.
.IP
The effective user
.SM ID
of the process
does not match the user
.SM ID
of the owner of the file,
and the effective group
.SM ID
of the process
does not match the group
.SM ID
of the file,
and the appropriate access bit of the ``other'' portion (07) of the
file mode is set.
.PP
Otherwise, the corresponding permissions are denied.
.SS "Message Queue Identifier"
A message queue identifier (msqid) is a unique positive integer created by a
.IR msgget (2)
system call.
Each msqid has a message queue and a data structure associated with it.
The data structure is referred to as
.I msqid_ds
and contains the following members:
.PP
.RS
.ta 8n 28n
.nf
struct	ipc_perm msg_perm;	/\(** operation permission struct \(**/
ushort	msg_cbytes;	/\(** current number of bytes on q \(**/
ushort	msg_qnum;	/\(** number of msgs on q \(**/
ushort	msg_qbytes;	/\(** max number of bytes on q \(**/
ushort	msg_lspid;	/\(** pid of last msgsnd operation \(**/
ushort	msg_lrpid;	/\(** pid of last msgrcv operation \(**/
time_t	msg_stime;	/\(** last msgsnd time \(**/
time_t	msg_rtime;	/\(** last msgrcv time \(**/
time_t	msg_ctime;	/\(** last change time \(**/
		/\(** Times measured in secs since \(**/
		/\(** 00:00:00 \s-1GMT\s+1, Jan. 1, 1970 \(**/
.fi
.RE
.PP
.B Msg_perm
is an ipc_perm structure that
specifies the message operation permission (see below).
This structure includes the following members:
.PP
.RS
.ta 8n 20n
.nf
ushort	cuid;	/\(** creator user id \(**/
ushort	cgid;	/\(** creator group id \(**/
ushort	uid;	/\(** user id \(**/
ushort	gid;	/\(** group id \(**/
ushort	mode;	/\(** r/w permission \(**/
.PP
.fi
.RE
.B Msg_cbytes
is the current number of bytes on the queue.
.B Msg_qnum
is the number of messages currently on the queue.
.B Msg_qbytes
is the maximum number of bytes allowed on the queue.
.B Msg_lspid
is the process id of the last process that performed a
.IR msgsnd " operation."
.B Msg_lrpid
is the process id of the last process that performed a
.IR msgrcv " operation."
.B Msg_stime
is the time of the last
.I msgsnd
operation,
.B msg_rtime
is the time of the last
.I msgrcv
operation, and
.B msg_ctime
is the time of the last
.IR msgctl (2)
operation that changed a member of the above structure.
.SS "Message Operation Permissions"
In the
.IR msgop "(2) and " msgctl (2)
system call descriptions, the permission required
for an operation is given as "{token}", where "token" is the type
of permission needed interpreted as follows:
.PP
.RS 0.75i
.PD 0
.TP 1.50i
00400
Read by user
.TP
00200
Write by user
.TP
00060
Read, Write by group
.TP
00006
Read, Write by others
.RE
.PD
.PP
Read and Write permissions on a msqid are
granted to a process if one or more of the following are true:
.IP
The effective user
.SM ID
of the process
is super-user.
.IP
The effective user
.SM ID
of the process
matches
.B msg_perm.[c]uid
in the data structure associated with
.I msqid
and the appropriate bit of the
``user'' portion (0600) of
.B msg_perm.mode
is set.
.IP
The effective user
.SM ID
of the process
does not match
.B msg_perm.[c]uid
and the effective group
.SM ID
of the process
matches
.B msg_perm.[c]gid
and the appropriate bit of the ``group'' portion
(060) of
.B msg_perm.mode
is set.
.IP
The effective user
.SM ID
of the process
does not match
.B msg_perm.[c]uid
and the effective group
.SM ID
of the process
does not match
.B msg_perm.[c]gid
and the appropriate bit of the ``other'' portion (06) of
.B msg_perm.mode
is set.
.PP
Otherwise, the corresponding permissions are denied.
.SS "Semaphore Identifier"
A semaphore identifier (semid) is a unique positive integer created by a
.IR semget (2)
system call.
Each semid has a set of semaphores and a data structure associated with it.
The data structure is referred to as
.I semid_ds
and contains the following members:
.PP
.RS
.ta 8n 28n
.nf
struct	ipc_perm sem_perm;	/\(** operation permission struct \(**/
ushort	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 \s-1GMT\s+1, Jan. 1, 1970 \(**/
.fi
.RE
.PP
.B Sem_perm
is an ipc_perm structure that
specifies the semaphore operation permission (see below).
This structure includes the following members:
.PP
.RS
.ta 8n 20n
.nf
ushort	cuid;	/\(** creator user id \(**/
ushort	cgid;	/\(** creator group id \(**/
ushort	uid;	/\(** user id \(**/
ushort	gid;	/\(** group id \(**/
ushort	mode;	/\(** r/a permission \(**/
.PP
.fi
.RE
The value of
.B sem_nsems
is equal to the number of semaphores in the set.
Each semaphore in the set is referenced by a positive integer
referred to as a
.IR sem_num .
Sem_num values run sequentially from 0 to the value of sem_nsems minus 1.
.B Sem_otime
is the time of the last
.IR semop (2)
operation, and
.B sem_ctime
is the time of the last
.IR semctl (2)
operation that changed a member of the above structure.
.PP
A semaphore is a data structure that contains the following members:
.PP
.RS
.ta 8n 20n
.nf
ushort	semval;	/\(** semaphore value \(**/
short	sempid;	/\(** pid of last operation  \(**/
ushort	semncnt;	/\(** # awaiting semval > cval \(**/
ushort	semzcnt;	/\(** # awaiting semval = 0 \(**/
.fi
.RE
.PP
.B Semval
is a non-negative integer.
.B Sempid
is equal to the process
.SM ID
of the last process that performed a semaphore operation on this semaphore.
.B Semncnt
is a count of the number of processes that are currently suspended
awaiting this semaphore's semval to become greater than its current value.
.B Semzcnt
is a count of the number of processes that are currently suspended
awaiting this semaphore's semval to become zero.
.SS "Semaphore Operation Permissions"
In the
.IR semop "(2) and " semctl (2)
system call descriptions, the permission required
for an operation is given as "{token}", where "token" is the type
of permission needed interpreted as follows:
.PP
.RS 0.75i
.PD 0
.TP 1.50i
00400
Read by user
.TP
00200
Alter by user
.TP
00060
Read, Alter by group
.TP
00006
Read, Alter by others
.RE
.PD
.PP
Read and Alter permissions on a semid are
granted to a process if one or more of the following are true:
.IP
The effective user
.SM ID
of the process
is super-user.
.IP
The effective user
.SM ID
of the process
matches
.B sem_perm.[c]uid
in the data structure associated with
.I semid
and the appropriate bit of the
``user'' portion (0600) of
.B sem_perm.mode
is set.
.IP
The effective user
.SM ID
of the process
does not match
.B sem_perm.[c]uid
and the effective group
.SM ID
of the process
matches
.B sem_perm.[c]gid
and the appropriate bit of the ``group'' portion
(060) of
.B sem_perm.mode
is set.
.IP
The effective user
.SM ID
of the process
does not match
.B sem_perm.[c]uid
and the effective group
.SM ID
of the process
does not match
.B sem_perm.[c]gid
and the appropriate bit of the ``other'' portion (06) of
.B sem_perm.mode
is set.
.PP
Otherwise, the corresponding permissions are denied.
.SS "Shared Memory Identifier"
A shared memory identifier (shmid) is a unique positive integer created by a
.IR shmget (2)
system call.
Each shmid has a segment of memory (referred to as a shared memory segment)
and a data structure associated with it.
The data structure is referred to as
.I shmid_ds
and contains the following members:
.PP
.RS
.ta 8n 28n
.nf
struct	ipc_perm shm_perm;	/\(** operation permission struct \(**/
int	shm_segsz;	/\(** size of segment \(**/
struct	proc *shm_perm;	/\(** address of linked proc \(**/
short	shm_pidx;	/\(** index of this segment \(**/
ushort	shm_cpid;	/\(** creator pid \(**/
ushort	shm_lpid;	/\(** pid of last operation \(**/
short	shm_cnattch;	/\(** number of loaded attaches \(**/
short	shm_nattch;	/\(** number of current attaches \(**/
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 \s-1GMT\s+1, Jan. 1, 1970 \(**/
.fi
.RE
.PP
.B Shm_perm
is an ipc_perm structure that
specifies the shared memory operation permission (see below).
This structure includes the following members:
.PP
.RS
.ta 8n 20n
.nf
ushort	cuid;	/\(** creator user id \(**/
ushort	cgid;	/\(** creator group id \(**/
ushort	uid;	/\(** user id \(**/
ushort	gid;	/\(** group id \(**/
ushort	mode;	/\(** r/w permission \(**/
.PP
.fi
.RE
.B Shm_segsz
specifies the size of the shared memory segment.
.B Shm_proc
is the address of the first process linked to this segment.
.B Shm_pidx
is the index of this shared memory segment in the shared memory table belonging
to that process.
.B Shm_cpid
is the process id of the process that created the shared memory identifier.
.B Shm_lpid
is the process id of the last process that performed a
.IR shmop "(2) operation."
.B Shm_cnattch
is the number of in-core processes attached to this segment.
.B Shm_nattch
is the number of processes that currently have this segment attached.
.B Shm_atime
is the time of the last
.I shmat
operation,
.B shm_dtime
is the time of the last
.I shmdt
operation,
and
.B shm_ctime
is the time of the last
.IR shmctl (2)
operation that changed one of the members of the above structure.
.SS "Shared Memory Operation Permissions"
In the
.IR shmop "(2) and " shmctl (2)
system call descriptions, the permission required
for an operation is given as "{token}", where "token" is the type
of permission needed interpreted as follows:
.PP
.RS 0.75i
.PD 0
.TP 1.50i
00400
Read by user
.TP
00200
Write by user
.TP
00060
Read, Write by group
.TP
00006
Read, Write by others
.RE
.PD
.PP
Read and Write permissions on a shmid are
granted to a process if one or more of the following are true:
.IP
The effective user
.SM ID
of the process
is super-user.
.IP
The effective user
.SM ID
of the process
matches
.B shm_perm.[c]uid
in the data structure associated with
.I shmid
and the appropriate bit of the
``user'' portion (0600) of
.B shm_perm.mode
is set.
.IP
The effective user
.SM ID
of the process
does not match
.B shm_perm.[c]uid
and the effective group
.SM ID
of the process
matches
.B shm_perm.[c]gid
and the appropriate bit of the ``group'' portion
(060) of
.B shm_perm.mode
is set.
.IP
The effective user
.SM ID
of the process
does not match
.B shm_perm.[c]uid
and the effective group
.SM ID
of the process
does not match
.B shm_perm.[c]gid
and the appropriate bit of the ``other'' portion (06) of
.B shm_perm.mode
is set.
.PP
Otherwise, the corresponding permissions are denied.
.SS "System Five Interfaces Library"
The following system calls constitute the system 5 interfaces library:
.PP
.RS
.IR msgctl ,
.br
.IR msgget ,
.br
.IR msgrcv ,
.br
.IR msgsnd ,
.br
.IR plock ,
.br
.IR semctl ,
.br
.IR semget ,
.br
.IR semop ,
.br
.IR shmat ,
.br
.IR shmctl ,
.br
.IR shmdt ,
.br
.IR shmget ,
.br
.IR ulimit ,
.br
.IR uname ,
.br
.IR ustat ,
.RE
.SH NOTES
This manual page replaces the 4.2BSD manual page.
.SH FILES
.nf
/usr/lib/libsys5.a	System Five Interfaces Library
.fi
.SH SEE ALSO
close(2),
ioctl(2),
open(2),
pipe(2),
read(2),
write(2),
intro(3).
.\"	@(#)intro.2	6.2 of 9/6/83

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.