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 condition
is indicated by an otherwise impossible return value. This is almost
always -1 or the null pointer; the individual descriptions specify 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
specified 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
detection 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 numbers.
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 document
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
corresponds 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 signal,
it will appear as if the interrupted function 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 example, 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 condition; the
maximum size is a system parameter. On some
architectures, 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 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 document
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 differ
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 inappropriate
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
specifying 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 specified
by resource RLIMIT_FSIZEn; the file size exceeds
the maximum supported by the file system; 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 setting
or removing of record locks on a file cannot 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 generates a
signal; the error is returned if the signal 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 message 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, condition
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 canceled
before completion.


48 ENOTSUP
Not supported

This version of the system does not support this
feature. Future versions of the system may provide
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 allocation 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-
specific 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 indeterminate.
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 structures were
available. This is a temporary condition; 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 permission 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
corrupted.


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 characters
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
protocol 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 network.


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 sufficient
buffer space or because a queue was full.


133 EISCONN
Transport endpoint is already connected

A connect request was made on an already connected
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
properly 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 session
that has established a connection with a controlling terminal.

Controlling Process


A session leader that established a connection to a controlling terminal.

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
hardware 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
condition 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
terminal will distinguish one process group of the session as the
foreground process group of the controlling terminal. This group has
certain 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 pathconf(2)
with the name argument _PC_LIMIT.

Masks


The file mode creation mask of the process used during any create
function 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 structure
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 performed
a msgsnd() operation.


The msg_lrpid member is the process id of the last process that performed
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
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 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 output
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 constructing
them and for connecting multiplexed configurations of streams.

Offset Maximum


An offset maximum is an attribute of an open file description
representing 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
directory.


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 running 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 lifetime, 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
identified 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
processor sets. A process bound to one of these sets will run only on
processors 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 messages
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 responsible
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 directory
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 structure
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 semaphore
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
currently 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
currently 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" portion
(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
session 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 session
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 performed
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
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 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" portion
(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
services 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
routines, 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 functions
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 messages
moving downstream.

ACKNOWLEDGMENTS


Sun Microsystems, Inc. gratefully acknowledges The Open Group for
permission to reproduce portions of its copyrighted documentation.
Original 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 documentation.


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 Interface
(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
versions 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.opengroup.org/unix/online.html.


This notice shall appear on any product containing this material.

SEE ALSO


standards(5), threads(5)


November 17, 2008 INTRO(2)