man pages section 2: System Calls

Intro(2)

Name | Synopsis | Description | DEFINITIONS | See Also

Name

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).

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:

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.
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.
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.
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 (2³¹ -1 bytes). For regular files that were opened with the O_LARGEFILE flag set, the offset maximum is 2⁶³ -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:

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

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

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