INTRO(2) — SYSTEM CALLS
NAME
intro − introduction to system calls and error numbers
SYNOPSIS
#include <errno.h>
DESCRIPTION
This section describes all of the system calls. A ‘(2V)’ heading indicates that the system call performs differently when called from programs that use the System V libraries (programs compiled using /usr/5bin/cc). On these pages, both the regular behavior and the System V behavior is described.
Most of these calls have one or more error returns. An error condition is indicated by an otherwise impossible return value. This is almost always ‘−1’; the individual descriptions specify the details. An error number is also made available in the external variable errno. errno is not cleared on successful calls, so it should be tested only after an error has been indicated. Note: a number of system calls overload the meanings of these error numbers, and the meanings must be interpreted according to the type and circumstances of the call.
As with normal arguments, all return codes and values from functions are of type integer unless otherwise noted.
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 given in <errno.h>.
Error 0
Unused.
1 EPERM 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.
2 ENOENT No such file or directory
This error occurs when a filename is specified and the file should exist but does not, or when one of the directories in a pathname does not exist.
3 ESRCH No such process
The process or process group whose number was given does not exist, or any such process is already dead.
4 EINTR Interrupted system call
An asynchronous signal (such as interrupt or quit) that the process has elected to catch occurred during a system call. If execution is resumed after processing the signal, and the system call is not restarted, it will appear as if the interrupted system call returned this error condition.
5 EIO I/O error
Some physical I/O error 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 that 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.
7 E2BIG Arg list too long
An argument list longer than 1,048,576 bytes is presented to execve(2) or a routine that called execve().
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 magic number (see a.out(5)).
9 EBADF Bad file number
Either a file descriptor refers to no open file, or a read (respectively, write) request is made to a file that is open only for writing (respectively, reading).
10 ECHILD No children
A wait(2) was executed by a process that had no existing or unwaited-for child processes.
11 EAGAIN No more processes
A fork(2) failed because the system’s process table is full or the user is not allowed to create any more processes, or a system call failed because of insufficient resources.
12 ENOMEM Not enough memory
During an execve(2), sbrk(), or brk(2), a program asks for more address space or swap space than the system is able to supply, or a process size limit would be exceeded. A lack of swap space is normally a temporary condition; however, a lack of address space is not a temporary condition. The maximum size of the text, data, and stack segments is a system parameter. Soft limits may be increased to their corresponding hard limits.
13 EACCES Permission denied
An attempt was made to access a file in a way forbidden by the protection system.
14 EFAULT Bad address
The system encountered a hardware fault in attempting to access the arguments of a system call.
15 ENOTBLK Block device required
A file that is not a block device was mentioned where a block device was required, for example, in mount(2).
16 EBUSY Device busy
An attempt was made to mount a file system that was already mounted or an attempt was made to dismount a file system on which there is an active file (open file, mapped file, current directory, or mounted-on directory).
17 EEXIST File exists
An existing file was mentioned in an inappropriate context, for example, link(2).
18 EXDEV Cross-device link
A hard link to a file on another file system was attempted.
19 ENODEV No such device
An attempt was made to apply an inappropriate system call to a device (for example, an attempt to read a write-only device) or an attempt was made to use a device not configured by the system.
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 chdir(2).
21 EISDIR Is a directory
An attempt was made to write on a directory.
22 EINVAL Invalid argument
A system call was made with an invalid argument; for example, dismounting a non-mounted file system, mentioning an unknown signal in sigvec() or kill(), reading or writing a file for which lseek() has generated a negative pointer, or some other argument inappropriate for the call. Also set by math functions, see intro(3).
23 ENFILE File table overflow
The system’s table of open files is full, and temporarily no more open() calls can be accepted.
24 EMFILE Too many open files
A process tried to have more open files than the system allows a process to have. The customary configuration limit is 64 per process.
25 ENOTTY Inappropriate ioctl for device
The code used in an ioctl() call is not supported by the object that the file descriptor in the call refers to.
26 unused
27 EFBIG File too large
The size of a file exceeded the maximum file size (1,082,201,088 bytes).
28 ENOSPC No space left on device"
A write() to an ordinary file, the creation of a directory or symbolic link, or the creation of a directory entry failed because no more disk blocks are available on the file system, or the allocation of an inode for a newly created file failed because no more inodes are available on the file system.
29 ESPIPE Illegal seek
An lseek() was issued to a socket or pipe. This error may also be issued for other non-seekable devices.
30 EROFS Read-only file system
An attempt to modify a file or directory was made on a file system mounted read-only.
31 EMLINK Too many links
An attempt was made to make more than 32767 hard links to a file.
32 EPIPE Broken pipe
An attempt was made to write on a pipe or socket for which there is no process to read the data. This condition normally generates a signal; the error is returned if the signal is caught or ignored.
33 EDOM Math argument
The argument of a function in the math library (as described in section 3M) is out of the domain of the function.
34 ERANGE Result too large
The value of a function in the math library (as described in section 3M) is unrepresentable within machine precision.
35 EWOULDBLOCK Operation would block
An operation that would cause a process to block was attempted on an object in non-blocking mode (see ioctl(2)).
36 EINPROGRESS Operation now in progress
An operation that takes a long time to complete (such as a connect(2)) was attempted on a non-blocking object (see ioctl(2)).
37 EALREADY Operation already in progress
An operation was attempted on a non-blocking object that already had an operation in progress.
38 ENOTSOCK Socket operation on non-socket
Self-explanatory.
39 EDESTADDRREQ Destination address required
A required address was omitted from an operation on a socket.
40 EMSGSIZE Message too long
A message sent on a socket was larger than the internal message buffer.
41 EPROTOTYPE Protocol wrong type for socket
A protocol was specified that does not support the semantics of the socket type requested. For example, you cannot use the ARPA Internet UDP protocol with type SOCK_STREAM.
42 ENOPROTOOPT Option not supported by protocol
A bad option was specified in a setsockopt() or getsockopt(2) call.
43 EPROTONOSUPPORT Protocol not supported
The protocol has not been configured into the system or no implementation for it exists.
44 ESOCKTNOSUPPORT Socket type not supported
The support for the socket type has not been configured into the system or no implementation for it exists.
45 EOPNOTSUPP Operation not supported on socket
For example, trying to accept a connection on a datagram socket.
46 EPFNOSUPPORT Protocol family not supported
The protocol family has not been configured into the system or no implementation for it exists.
47 EAFNOSUPPORT Address family not supported by protocol family
An address incompatible with the requested protocol was used. For example, you should not necessarily expect to be able to use PUP Internet addresses with ARPA Internet protocols.
48 EADDRINUSE Address already in use
Only one usage of each address is normally permitted.
49 EADDRNOTAVAIL Can’t assign requested address
Normally results from an attempt to create a socket with an address not on this machine.
50 ENETDOWN Network is down
A socket operation encountered a dead network.
51 ENETUNREACH Network is unreachable
A socket operation was attempted to an unreachable network.
52 ENETRESET Network dropped connection on reset
The host you were connected to crashed and rebooted.
53 ECONNABORTED Software caused connection abort
A connection abort was caused internal to your host machine.
54 ECONNRESET Connection reset by peer
A connection was forcibly closed by a peer. This normally results from the peer executing a shutdown(2) call.
55 ENOBUFS No buffer space available
An operation on a socket or pipe was not performed because the system lacked sufficient buffer space.
56 EISCONN Socket is already connected
A connect() request was made on an already connected socket; or, a sendto() or sendmsg() request on a connected socket specified a destination other than the connected party.
57 ENOTCONN Socket is not connected
An request to send or receive data was disallowed because the socket is not connected.
58 ESHUTDOWN Can’t send after socket shutdown
A request to send data was disallowed because the socket had already been shut down with a previous shutdown(2) call.
59 unused
60 ETIMEDOUT Connection timed out
A connect request or an NFS request failed because the party to which the request was made did not properly respond after a period of time. (The timeout period is dependent on the communication protocol.)
61 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 foreign host.
62 ELOOP Too many levels of symbolic links
A pathname lookup involved more than 20 symbolic links.
63 ENAMETOOLONG File name too long
A component of a pathname exceeded 255 characters, or an entire pathname exceeded 1024 characters.
64 EHOSTDOWN Host is down
A socket operation failed because the destination host was down.
65 EHOSTUNREACH Host is unreachable
A socket operation was attempted to an unreachable host.
66 ENOTEMPTY Directory not empty
An attempt was made to remove a directory with entries other than ‘.’ and ‘..’ by performing a rmdir() system call or a rename() system call with that directory specified as the target directory.
67 unused
68 unused
69 EDQUOT Disc quota exceeded
A write() 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.
70 ESTALE Stale NFS file handle
An NFS client referenced a file that it had opened but that had since been deleted.
71 EREMOTE Too many levels of remote in path
An attempt was made to remotely mount a file system into a path that already has a remotely mounted component.
72 ENOSTR Not a stream device
A putmsg(2) or getmsg(2) system call was attempted on a file descriptor that is not a STREAMS device.
73 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(2) operation is indeterminate.
74 ENOSR Out of stream resources
During a STREAMS open(2V), either no STREAMS queues or no STREAMS head data structures were available.
75 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 msgop(2).
76 EBADMSG Not a data message
During a read(2), getmsg(2), or ioctl(2) I_RECVFD system call to a STREAMS device, something has come to the head of the queue that cannot be processed. That something depends on the system call:
read(2) control information or a passed file descriptor.
getmsg(2)
passed file descriptor.
ioctl(2) control or data information.
77 EIDRM Identifier removed
This error is returned to processes that resume execution due to the removal of an identifier from the
78 unused
79 ENOLCK No locks available
A system-imposed limit on the number of simultaneous file and record locks was reached and no more were available at that time. IPC system’s name space (see msgctl(2), semctl(2), and shmctl(2)).
DEFINITIONS
Descriptor
An integer assigned by the system when a file is referenced by open(2V), dup(2), or pipe(2) or a socket is referenced by socket(2) or socketpair(2) that uniquely identifies an access path to that file or socket from a given process or any of its children.
Directory
A directory is a special type of file that contains entries that are references to other files. Directory entries are called links. By convention, a directory contains at least two links, ‘.’ and ‘..’, referred to as dot and dot-dot respectively. Dot refers to the directory itself and dot-dot refers to its parent directory.
Effective User ID, Effective Group ID, and Access Groups
Access to system resources is governed by three values: the effective user ID, the effective group ID, and the group access list.
The effective user ID and effective group ID are initially the process’s real user ID and real group ID respectively. Either may be modified through execution of a set-user-ID or set-group-ID file (possibly by one of its ancestors) (see execve(2)).
The group access list is an additional set of group ID’s used only in determining resource accessibility. Access checks are performed as described below in File Access Permissions.
File Access Permissions
Every file in the file system has a set of access permissions. These permissions are used in determining whether a process may perform a requested operation on the file (such as opening a file for writing). Access permissions are established at the time a file is created. They may be changed at some later time through the chmod(2) call.
File access is broken down according to whether a file may be: read, written, or executed. Directory files use the execute permission to control if the directory may be searched.
File access permissions are interpreted by the system as they apply to three different classes of users: the owner of the file, those users in the file’s group, anyone else. Every file has an independent set of access permissions for each of these classes. When an access check is made, the system decides if permission should be granted by checking the access information applicable to the caller.
Read, write, and execute/search permissions on a file are granted to a process if:
The process’s effective user ID is that of the super-user.
The process’s effective user ID matches the user ID of the owner of the file and the owner permissions allow the access.
The process’s effective user ID does not match the user ID of the owner of the file, and either the process’s effective group ID matches the group ID of the file, or the group ID of the file is in the process’s group access list, and the group permissions allow the access.
Neither the effective user ID nor effective group ID and group access list of the process match the corresponding user ID and group ID of the file, but the permissions for “other users” allow access.
Otherwise, permission is denied.
File Name
Names consisting of up to 255 characters may be used to name an ordinary file, special file, or directory.
These characters may be selected from the set of all ASCII character excluding \0 (null) and the ASCII code for / (slash). (The parity bit, bit 8, must be 0.)
Note: it is generally unwise to use ∗, ?, [, or ] as part of filenames because of the special meaning attached to these characters by the shell. See sh(1). Although permitted, it is advisable to avoid the use of unprintable characters in filenames.
Message Queue Identifier
A message queue identifier (msqid) is a unique positive integer created by a msgget(2) system 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:
structipc_perm msg_perm; /∗ operation permission struct ∗/
ushortmsg_qnum;/∗ number of msgs on q ∗/
ushortmsg_qbytes;/∗ max number of bytes on q ∗/
ushortmsg_lspid;/∗ pid of last msgsnd operation ∗/
ushortmsg_lrpid;/∗ pid of last msgrcv operation ∗/
time_tmsg_stime;/∗ last msgsnd time ∗/
time_tmsg_rtime;/∗ last msgrcv time ∗/
time_tmsg_ctime;/∗ last change time ∗/
/∗ Times measured in secs since ∗/
/∗ 00:00:00 GMT, Jan. 1, 1970 ∗/
msg_perm() is an ipc_perm structure that specifies the message operation permission (see below). This structure includes the following members:
ushortcuid;/∗ creator user id ∗/
ushortcgid;/∗ creator group id ∗/
ushortuid;/∗ user id ∗/
ushortgid;/∗ group id ∗/
ushortmode;/∗ r/w permission ∗/
msg_qnum is the number of messages currently on the queue. msg_qbytes is the maximum number of bytes allowed on the queue. msg_lspid is the process ID of the last process that performed a msgsnd operation. msg_lrpid is the process ID of the last process that performed a msgrcv operation. msg_stime is the time of the last msgsnd operation, msg_rtime is the time of the last msgrcv operation, and msg_ctime is the time of the last msgctl(2) operation that changed a member of the above structure.
Message Operation Permissions
In the 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:
00400 Read by user
00200 Write by user
00060 Read, Write by group
00006 Read, Write by others
Read and Write permissions on a msqid are granted to a process if one or more of the following are true:
The effective user ID of the process is super-user.
The effective user ID of the process matches msg_perm.[c]uid in the data structure associated with msqid and the appropriate bit of the “user” portion (0600) of msg_perm.mode is set.
The effective user ID of the process does not match msg_perm.[c]uid and the effective group ID of the process matches msg_perm.[c]gid and the appropriate bit of the “group” portion (060) of msg_perm.mode is set.
The effective user ID of the process does not match msg_perm.[c]uid and the effective group ID of the process does not match msg_perm.[c]gid and the appropriate bit of the “other” portion (06) of msg_perm.mode is set.
Otherwise, the corresponding permissions are denied.
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.
Path Name and Path Prefix
A pathname 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 filename. The total length of a pathname must be less than {MAXPATHLEN} (1024) characters.
More precisely, a pathname is a null-terminated character string constructed as follows:
<path-name>::=<file-name>│<path-prefix><file-name>│/
<path-prefix>::=<rtprefix>│/<rtprefix>
<rtprefix>::=<dirname>/│<rtprefix><dirname>/
where <file-name> is a string of 1 to 255 characters other than the ASCII slash and null, and <dirname> is a string of 1 to 255 characters (other than the ASCII slash and null) that names a directory.
If a pathname begins with a slash, the search begins at the root directory. Otherwise, the search begins at the current working directory.
A slash, by itself, names the root directory. A dot (.) names the current working directory.
A null pathname also refers to the current directory. However, this is not true of all UNIX systems. (On such systems, accidental use of a null pathname in routines that do not check for it may corrupt the current working directory.) For portable code, specify the current directory explicitly using ‘"."’, rather than ‘""’.
Process Group ID
Each active process is a member of a process group that 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 killpg(2)) and the job control mechanisms of csh(1).
Process ID
Each active process in the system is uniquely identified by a positive integer called a process ID. The range of this ID is from 0 to 30000.
Real User ID and Real Group ID
Each user on the system is identified by a positive integer termed the real user ID.
Each user is also a member of one or more groups. One of these groups is distinguished from others and used in implementing accounting facilities. The positive integer corresponding to this distinguished group is termed the real group ID.
All processes have a real user ID and real group ID. These are initialized from the equivalent attributes of the process that created it.
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. A process’s root directory need not be the root directory of the root file system.
Semaphore Identifier
A semaphore identifier (semid) is a unique positive integer created by a 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 semid_ds and contains the following members:
structipc_perm sem_perm; /∗ operation permission struct ∗/
ushortsem_nsems;/∗ number of sems in set ∗/
time_tsem_otime;/∗ last operation time ∗/
time_tsem_ctime;/∗ last change time ∗/
/∗ Times measured in secs since ∗/
/∗ 00:00:00 GMT, Jan. 1, 1970 ∗/
sem_perm is an ipc_perm structure that specifies the semaphore operation permission (see below). This structure includes the following members:
ushortcuid;/∗ creator user id ∗/
ushortcgid;/∗ creator group id ∗/
ushortuid;/∗ user id ∗/
ushortgid;/∗ group id ∗/
ushortmode;/∗ r/a permission ∗/
The value of 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 sem_num. sem_num values run sequentially from 0 to the value of sem_nsems minus 1. sem_otime is the time of the last semop(2) operation, and sem_ctime is the time of the last semctl(2) operation that changed a member of the above structure.
A semaphore is a data structure that contains the following members:
ushortsemval;/∗ semaphore value ∗/
shortsempid;/∗ pid of last operation ∗/
ushortsemncnt;/∗ # awaiting semval > cval ∗/
ushortsemzcnt;/∗ # awaiting semval = 0 ∗/
semval is a non-negative integer. sempid is equal to the process ID of the last process that performed a semaphore operation on this semaphore. 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. semzcnt is a count of the number of processes that are currently suspended awaiting this semaphore’s semval to become zero.
Semaphore Operation Permissions
In the 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:
00400 Read by user
00200 Alter by user
00060 Read, Alter by group
00006 Read, Alter by others
Read and Alter permissions on a semid are granted to a process if one or more of the following are true:
The effective user ID of the process is super-user.
The effective user ID of the process matches sem_perm.[c]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 user ID of the process does not match sem_perm.[c]uid and the effective group ID of the process matches sem_perm.[c]gid and the appropriate bit of the “group” portion (060) of sem_perm.mode is set.
The effective user ID of the process does not match sem_perm.[c]uid and the effective group ID of the process does not match sem_perm.[c]gid and the appropriate bit of the “other” portion (06) of sem_perm.mode is set.
Otherwise, the corresponding permissions are denied.
Shared Memory Identifier
A shared memory identifier (shmid) is a unique positive integer created by a 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 shmid_ds and contains the following members:
structipc_perm shm_perm; /∗ operation permission struct ∗/
intshm_segsz;/∗ size of segment ∗/
ushortshm_cpid;/∗ creator pid ∗/
ushortshm_lpid;/∗ pid of last operation ∗/
shortshm_nattch;/∗ number of current attaches ∗/
time_tshm_atime;/∗ last attach time ∗/
time_tshm_dtime;/∗ last detach time ∗/
time_tshm_ctime;/∗ last change time ∗/
/∗ Times measured in secs since ∗/
/∗ 00:00:00 GMT, Jan. 1, 1970 ∗/
shm_perm is an ipc_perm structure that specifies the shared memory operation permission (see below). This structure includes the following members:
ushortcuid;/∗ creator user id ∗/
ushortcgid;/∗ creator group id ∗/
ushortuid;/∗ user id ∗/
ushortgid;/∗ group id ∗/
ushortmode;/∗ r/w permission ∗/
shm_segsz specifies the size of the shared memory segment. shm_cpid is the process ID of the process that created the shared memory identifier. shm_lpid is the process ID of the last process that performed a shmop(2) operation. shm_nattch is the number of processes that currently have this segment attached. shm_atime is the time of the last shmat operation, shm_dtime is the time of the last shmdt operation, and shm_ctime 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 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:
00400 Read by user
00200 Write by user
00060 Read, Write by group
00006 Read, Write by others
Read and Write permissions on a shmid are granted to a process if one or more of the following are true:
The effective user ID of the process is super-user.
The effective user ID of the process matches shm_perm.[c]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 user ID of the process does not match shm_perm.[c]uid and the effective group ID of the process matches shm_perm.[c]gid and the appropriate bit of the “group” portion (060) of shm_perm.mode is set.
The effective user ID of the process does not match shm_perm.[c]uid and the effective group ID of the process does not match shm_perm.[c]gid and the appropriate bit of the “other” portion (06) of shm_perm.mode is set.
Otherwise, the corresponding permissions are denied.
Sockets and Address Families
A socket is an endpoint for communication between processes. Each socket has queues for sending and receiving data.
Sockets are typed according to their communications properties. These properties include whether messages sent and received at a socket require the name of the partner, whether communication is reliable, the format used in naming message recipients, etc.
Each instance of the system supports some collection of socket types; consult socket(2) for more information about the types available and their properties.
Each instance of the system supports some number of sets of communications protocols. Each protocol set supports addresses of a certain format. An Address Family is the set of addresses for a specific group of protocols. Each socket has an address chosen from the address family in which the socket was created.
Special Processes
The processes with a process ID’s of 0, 1, and 2 are special. Process 0 is the scheduler. Process 1 is the initialization process init, and is the ancestor of every other process in the system. It is used to control the process structure. Process 2 is the paging daemon.
Super-user
A process is recognized as a super-user process and is granted special privileges if its effective user ID is 0.
Tty Group ID
Each active process can be a member of a terminal group that is identified by a positive integer called the tty group ID. This grouping is used to arbitrate between multiple jobs contending for the same terminal (see csh(1), and termio(4), and to terminate a group of related processes upon termination of one of the processes in the group (see exit(2) and sigvec(2)).
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 principle functions of the stream head are processing STREAMS-related system calls, and passing data and information between a user process and the stream.
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 emulator, and need not be associated with a hardware device.
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.
Downstream
In a stream, the direction from stream head to driver.
Upstream
In a stream, the direction from driver to stream head.
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.
Read Queue
In a stream, the message queue in a module or driver containing messages moving upstream.
Write Queue
In a stream, the message queue in a module or driver containing messages moving downstream.
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.
SEE ALSO
csh(1), sh(1), brk(2), chdir(2), chmod(2), connect(2), dup(2), execve(2), exit(2), fork(2), getmsg(2), getsockopt(2), ioctl(2), killpg(2), link(2), mount(2), msgctl(2), msgget(2), msgop(2), open(2V), pipe(2), putmsg(2), read(2), semctl(2), semget(2), semop(2), setsockopt(2), shmctl(2), shmget(2), shmop(2), shutdown(2), sigvec(2), socket(2), socketpair(2), wait(2), intro(3), perror(3) termio(4), a.out(5)
LIST OF SYSTEM CALLS
NameAppears on PageDescription
_exit()exit(2) terminate a process
accept()accept(2) accept a connection on a socket
access()access(2) determine accessibility of file
acct()acct(2) turn accounting on or off
adjtime()adjtime(2) correct the time to allow synchronization of the system clock
async_daemon()nfssvc(2) NFS daemons
audit()audit(2) write a record to the audit log
auditon()auditon(2) manipulate auditing
auditsvc()auditsvc(2) write audit records to specified file descriptor
bind()bind(2) bind a name to a socket
brk()brk(2) change data segment size
chdir()chdir(2) change current working directory
chmod()chmod(2) change mode of file
chown()chown(2) change owner and group of a file
chroot()chroot(2) change root directory
close()close(2) delete a descriptor
connect()connect(2) initiate a connection on a socket
creat()creat(2) create a new file
dup2()dup(2) duplicate a descriptor
dup()dup(2) duplicate a descriptor
execve()execve(2) execute a file
fchmod()chmod(2) change mode of file
fchown()chown(2) change owner and group of a file
fcntl()fcntl(2V) file control
flock()flock(2) apply or remove an advisory lock on an open file
fork()fork(2) create a new process
fstat()stat(2) get file status
fsync()fsync(2) synchronize a file’s in-core state with that on disk
ftruncate()truncate(2) set a file to a specified length
getauid()getauid(2) get and set user audit identity
getdents()getdents(2) gets directory entries in a filesystem independent format
getdirentries()getdirentries(2) gets directory entries in a filesystem independent format
getdomainname()getdomainname(2) get/set name of current domain
getdtablesize()getdtablesize(2) get descriptor table size
getegid()getgid(2) get group identity
geteuid()getuid(2) get user identity
getgid()getgid(2) get group identity
getgroups()getgroups(2) get or set group access list
gethostid()gethostid(2) get unique identifier of current host
gethostname()gethostname(2) get/set name of current host
getitimer()getitimer(2) get/set value of interval timer
getmsg()getmsg(2) get next message off a stream
getpagesize()getpagesize(2) get system page size
getpeername()getpeername(2) get name of connected peer
getpgrp()setpgrp(2V) set and/or return the process group of a process
getpid()getpid(2) get process identification
getppid()getpid(2) get process identification
getpriority()getpriority(2) get/set program scheduling priority
getrlimit()getrlimit(2) control maximum system resource consumption
getrusage()getrusage(2) get information about resource utilization
getsockname()getsockname(2) get socket name
getsockopt()getsockopt(2) get and set options on sockets
gettimeofday()gettimeofday(2) get or set the date and time
getuid()getuid(2) get user identity
ioctl()ioctl(2) control device
kill()kill(2V) send a signal to a process or a group of processes
killpg()killpg(2) send signal to a process group
link()link(2) make a hard link to a file
listen()listen(2) listen for connections on a socket
lseek()lseek(2) move read/write pointer
lstat()stat(2) get file status
mincore()mincore(2) determine residency of memory pages
mkdir()mkdir(2) make a directory file
mknod()mknod(2) make a special file
mmap()mmap(2) map pages of memory
mount()mount(2) mount file system
mprotect()mprotect(2) set protection of memory mapping
msgctl()msgctl(2) message control operations
msgget()msgget(2) get message queue
msgop()msgop(2) message operations
msgrcv()msgop(2) message operations
msgsnd()msgop(2) message operations
msync()msync(2) synchronize memory with physical storage
munmap()munmap(2) unmap pages of memory.
nfssvc()nfssvc(2) NFS daemons
open()open(2V) open or create a file for reading or writing
pipe()pipe(2) create an interprocess communication channel
poll()poll(2) STREAMS input/output multiplexing
profil()profil(2) execution time profile
ptrace()ptrace(2) process trace
putmsg()putmsg(2) send a message on a stream
quotactl()quotactl(2) manipulate disk quotas
read()read(2V) read input
readlink()readlink(2) read value of a symbolic link
readv()read(2V) read input
reboot()reboot(2) reboot system or halt processor
recv()recv(2) receive a message from a socket
recvfrom()recv(2) receive a message from a socket
recvmsg()recv(2) receive a message from a socket
rename()rename(2) change the name of a file
rmdir()rmdir(2) remove a directory file
sbrk()brk(2) change data segment size
select()select(2) synchronous I/O multiplexing
semctl()semctl(2) semaphore control operations
semget()semget(2) get set of semaphores
semop()semop(2) semaphore operations
send()send(2) send a message from a socket
sendmsg()send(2) send a message from a socket
sendto()send(2) send a message from a socket
setaudit()setuseraudit(2) set the audit classes for a specified user ID
setauid()getauid(2) get and set user audit identity
setdomainname()getdomainname(2) get/set name of current domain
setgroups()getgroups(2) get or set group access list
sethostname()gethostname(2) get/set name of current host
setitimer()getitimer(2) get/set value of interval timer
setpgrp()setpgrp(2V) set and/or return the process group of a process
setpriority()getpriority(2) get/set program scheduling priority
setregid()setregid(2) set real and effective group IDs
setreuid()setreuid(2) set real and effective user IDs
setrlimit()getrlimit(2) control maximum system resource consumption
setsockopt()getsockopt(2) get and set options on sockets
settimeofday()gettimeofday(2) get or set the date and time
setuseraudit()setuseraudit(2) set the audit classes for a specified user ID
shmat()shmop(2) shared memory operations
shmctl()shmctl(2) shared memory control operations
shmdt()shmop(2) shared memory operations
shmget()shmget(2) get shared memory segment identifier
shmop()shmop(2) shared memory operations
shutdown()shutdown(2) shut down part of a full-duplex connection
sigblock()sigblock(2) block signals
sigpause()sigpause(2) atomically release blocked signals and wait for interrupt
sigsetmask()sigsetmask(2) set current signal mask
sigstack()sigstack(2) set and/or get signal stack context
sigvec()sigvec(2) software signal facilities
socket()socket(2) create an endpoint for communication
socketpair()socketpair(2) create a pair of connected sockets
stat()stat(2) get file status
statfs()statfs(2) get file system statistics
swapon()swapon(2) add a swap device for interleaved paging/swapping
symlink()symlink(2) make symbolic link to a file
sync()sync(2) update super-block
syscall()syscall(2) indirect system call
tell()lseek(2) move read/write pointer
truncate()truncate(2) set a file to a specified length
umask()umask(2) set file creation mode mask
uname()uname(2V) get name of current system
unlink()unlink(2) remove directory entry
unmount()unmount(2) remove a file system
utimes()utimes(2) set file times
vadvise()vadvise(2) give advice to paging system
vfork()vfork(2) spawn new process in a virtual memory efficient way
vhangup()vhangup(2) virtually “hangup” the current control terminal
wait3()wait(2) wait for process to terminate or stop
wait4()wait(2) wait for process to terminate or stop
wait()wait(2) wait for process to terminate or stop
WIFEXITED()wait(2) wait for process to terminate or stop
WIFSIGNALED()wait(2) wait for process to terminate or stop
WIFSTOPPED()wait(2) wait for process to terminate or stop
write()write(2V) write output
writev()write(2V) write output
Sun Release 4.0 — Last change: 25 March 1989