Intro(2) System Calls Intro(2)NAME
Intro, intro - introduction to system calls and error numbers
SYNOPSIS
#include <errno.h>
DESCRIPTION
A system call is a C library function that requests a service from the
system, such as getting the time of day. This request is performed in
the kernel. The library interface executes a trap into the kernel,
which actually executes the system call code.
Most system calls return one or more error conditions. An error condi‐
tion is indicated by an otherwise impossible return value. This is
almost always −1 or the null pointer; the individual descriptions spec‐
ify the details. An error number is also made available in the external
variable errno, which is not cleared on successful calls, so it should
be tested only after an error has been indicated.
In the case of multithreaded applications, the -mt option must be spec‐
ified on the command line at compilation time (see threads(5)). When
the -mt option is specified, errno becomes a macro that enables each
thread to have its own errno. This errno macro can be used on either
side of the assignment as though it were a variable.
An error value listed as "will fail" describes a condition whose detec‐
tion and reporting is mandatory for an implementation that conforms to
the Single UNIX Specification (SUS). An application can rely on this
condition being detected and reported. An error value listed as "may
fail" describes a condition whose detection and reporting is optional
for an implementation that conforms to the SUS. An application should
not rely this condition being detected and reported. An application
that relies on such behavior cannot be assured to be portable across
conforming implementations. If more than one error occurs in processing
a function call, any one of the possible errors might may be returned,
as the order of detection is undefined. See standards(5) for additional
information regarding the Single UNIX Specification.
Each system call description attempts to list all possible error num‐
bers. The following is a complete list of the error numbers and their
names as defined in <errno.h>.
1 EPERM Lacking appropriate privileges
Typically this error indicates an attempt to
modify a file in some way forbidden except to
its owner or an appropriately privileged
process. It is also returned for attempts by
ordinary users to perform operations allowed
only to processes with certain privileges.
The manual pages for individual functions docu‐
ment which privileges are needed to override the
restriction.
2 ENOENT No such file or directory
A file name is specified and the file should
exist but doesn't, or one of the directories in
a path name does not exist.
3 ESRCH No such process, LWP, or thread
No process can be found in the system that cor‐
responds to the specified PID, LWPID_t, or
thread_t.
4 EINTR Interrupted system call
An asynchronous signal (such as interrupt or
quit), which the user has elected to catch,
occurred during a system service function. If
execution is resumed after processing the sig‐
nal, it will appear as if the interrupted func‐
tion call returned this error condition.
In a multithreaded application, EINTR may be
returned whenever another thread or LWP calls
fork(2).
5 EIO I/O error
Some physical I/O error has occurred. This error
may in some cases occur on a call following the
one to which it actually applies.
6 ENXIO No such device or address
I/O on a special file refers to a subdevice
which does not exist, or exists beyond the limit
of the device. It may also occur when, for exam‐
ple, a tape drive is not on-line or no disk pack
is loaded on a drive.
7 E2BIG Arg list too long
An argument list longer than ARG_MAX bytes is
presented to a member of the exec family of
functions (see exec(2)). The argument list limit
is the sum of the size of the argument list plus
the size of the environment's exported shell
variables.
8 ENOEXEC Exec format error
A request is made to execute a file which,
although it has the appropriate permissions,
does not start with a valid format (see
a.out(4)).
9 EBADF Bad file number
Either a file descriptor refers to no open file,
or a read(2) (respectively, write(2)) request
is made to a file that is open only for writing
(respectively, reading).
10 ECHILD No child processes
A wait(3C) function call was executed by a
process that had no existing or unwaited-for
child processes.
11 EAGAIN No more processes, or no more LWPs
For example, the fork(2) function failed because
the system's process table is full or the user
is not allowed to create any more processes, or
a call failed because of insufficient memory or
swap space.
12 ENOMEM Not enough space
During execution of brk() or sbrk() (see
brk(2)), or one of the exec family of functions,
a program asks for more space than the system is
able to supply. This is not a temporary condi‐
tion; the maximum size is a system parameter. On
some architectures, the error may also occur if
the arrangement of text, data, and stack seg‐
ments requires too many segmentation registers,
or if there is not enough swap space during the
fork(2) function.
13 EACCES Permission denied
An attempt was made to access a file in a way
forbidden by the protection system.
The manual pages for individual functions docu‐
ment which privileges are needed to override the
protection system.
14 EFAULT Bad address
The system encountered a hardware fault in
attempting to use an argument of a routine. For
example, errno potentially may be set to EFAULT
any time a routine that takes a pointer argument
is passed an invalid address, if the system can
detect the condition. Because systems will dif‐
fer in their ability to reliably detect a bad
address, on some implementations passing a bad
address to a routine will result in undefined
behavior.
15 ENOTBLK Block device required
A non-block device or file was mentioned where a
block device was required (for example, in a
call to the mount(2) function).
16 EBUSY Device busy
An attempt was made to mount a device that was
already mounted or an attempt was made to
unmount a device on which there is an active
file (open file, current directory, mounted-on
file, active text segment). It will also occur
if an attempt is made to enable accounting when
it is already enabled. The device or resource is
currently unavailable. EBUSY is also used by
mutexes, semaphores, condition variables, and
r/w locks, to indicate that a lock is held,
and by the processor control function P_ONLINE.
17 EEXIST File exists
An existing file was mentioned in an inappropri‐
ate context (for example, call to the link(2)
function).
18 EXDEV Cross-device link
A hard link to a file on another device was
attempted.
19 ENODEV No such device
An attempt was made to apply an inappropriate
operation to a device (for example, read a
write-only device).
20 ENOTDIR Not a directory
A non-directory was specified where a directory
is required (for example, in a path prefix or as
an argument to the chdir(2) function).
21 EISDIR Is a directory
An attempt was made to write on a directory.
22 EINVAL Invalid argument
An invalid argument was specified (for example,
unmounting a non-mounted device), mentioning an
undefined signal in a call to the signal(3C) or
kill(2) function, or an unsupported operation
related to extended attributes was attempted.
23 ENFILE File table overflow
The system file table is full (that is,
SYS_OPEN files are open, and temporarily no more
files can be opened).
24 EMFILE Too many open files
No process may have more than OPEN_MAX file
descriptors open at a time.
25 ENOTTY Inappropriate ioctl for device
A call was made to the ioctl(2) function speci‐
fying a file that is not a special character
device.
26 ETXTBSY Text file busy (obsolete)
An attempt was made to execute a pure-procedure
program that is currently open for writing. Also
an attempt to open for writing or to remove a
pure-procedure program that is being executed.
(This message is obsolete.)
27 EFBIG File too large
The size of the file exceeded the limit speci‐
fied by resource RLIMIT_FSIZEn; the file size
exceeds the maximum supported by the file sys‐
tem; or the file size exceeds the offset maximum
of the file descriptor. See the File Descriptor
subsection of the DEFINITIONS section below.
28 ENOSPC No space left on device
While writing an ordinary file or creating a
directory entry, there is no free space left on
the device. In the fcntl(2) function, the set‐
ting or removing of record locks on a file can‐
not be accomplished because there are no more
record entries left on the system.
29 ESPIPE Illegal seek
A call to the lseek(2) function was issued to a
pipe.
30 EROFS Read-only file system
An attempt to modify a file or directory was
made on a device mounted read-only.
31 EMLINK Too many links
An attempt to make more than the maximum number
of links, LINK_MAX, to a file.
32 EPIPE Broken pipe
A write on a pipe for which there is no process
to read the data. This condition normally gener‐
ates a signal; the error is returned if the sig‐
nal is ignored.
33 EDOM Math argument out of domain of function
The argument of a function in the math package
(3M) is out of the domain of the function.
34 ERANGE Math result not representable
The value of a function in the math package (3M)
is not representable within machine precision.
35 ENOMSG No message of desired type
An attempt was made to receive a message of a
type that does not exist on the specified mes‐
sage queue (see msgrcv(2)).
36 EIDRM Identifier removed
This error is returned to processes that resume
execution due to the removal of an identifier
from the file system's name space (see
msgctl(2), semctl(2), and shmctl(2)).
37 ECHRNG Channel number out of range
38 EL2NSYNC Level 2 not synchronized
39 EL3HLT Level 3 halted
40 EL3RST Level 3 reset
41 ELNRNG Link number out of range
42 EUNATCH Protocol driver not attached
43 ENOCSI No CSI structure available
44 EL2HLT Level 2 halted
45 EDEADLK Deadlock condition
A deadlock situation was detected and avoided.
This error pertains to file and record locking,
and also applies to mutexes, semaphores, condi‐
tion variables, and r/w locks.
46 ENOLCK No record locks available
There are no more locks available. The system
lock table is full (see fcntl(2)).
47 ECANCELED Operation canceled
The associated asynchronous operation was can‐
celed before completion.
48 ENOTSUP Not supported
This version of the system does not support this
feature. Future versions of the system may pro‐
vide support.
49 EDQUOT Disc quota exceeded
A write(2) to an ordinary file, the creation of
a directory or symbolic link, or the creation of
a directory entry failed because the user's
quota of disk blocks was exhausted, or the allo‐
cation of an inode for a newly created file
failed because the user's quota of inodes was
exhausted.
58-59 Reserved
60 ENOSTR Device not a stream
A putmsg(2) or getmsg(2) call was attempted on a
file descriptor that is not a STREAMS device.
61 ENODATA No data available
62 ETIME Timer expired
The timer set for a STREAMS ioctl(2) call has
expired. The cause of this error is device-spe‐
cific and could indicate either a hardware or
software failure, or perhaps a timeout value
that is too short for the specific operation.
The status of the ioctl() operation is indeter‐
minate. This is also returned in the case of
_lwp_cond_timedwait(2) or cond_timedwait(3C).
63 ENOSR Out of stream resources
During a STREAMS open(2) call, either no
STREAMS queues or no STREAMS head data struc‐
tures were available. This is a temporary condi‐
tion; one may recover from it if other processes
release resources.
65 ENOPKG Package not installed
This error occurs when users attempt to use a
call from a package which has not been
installed.
71 EPROTO Protocol error
Some protocol error occurred. This error is
device-specific, but is generally not related to
a hardware failure.
77 EBADMSG Not a data message
During a read(2), getmsg(2), or ioctl(2)
I_RECVFD call to a STREAMS device, something has
come to the head of the queue that can not be
processed. That something depends on the call:
read(): control information or passed file
descriptor.
getmsg(): passed file descriptor.
ioctl(): control or data information.
78 ENAMETOOLONG File name too long
The length of the path argument exceeds
PATH_MAX, or the length of a path component
exceeds NAME_MAX while _POSIX_NO_TRUNC is in
effect; see limits.h(3HEAD).
79 EOVERFLOW Value too large for defined data type.
80 ENOTUNIQ Name not unique on network
Given log name not unique.
81 EBADFD File descriptor in bad state
Either a file descriptor refers to no open file
or a read request was made to a file that is
open only for writing.
82 EREMCHG Remote address changed
83 ELIBACC Cannot access a needed share library
Trying to exec an a.out that requires a static
shared library and the static shared library
does not exist or the user does not have permis‐
sion to use it.
84 ELIBBAD Accessing a corrupted shared library
Trying to exec an a.out that requires a static
shared library (to be linked in) and exec could
not load the static shared library. The static
shared library is probably corrupted.
85 ELIBSCN .lib section in a.out corrupted
Trying to exec an a.out that requires a static
shared library (to be linked in) and there was
erroneous data in the .lib section of the a.out.
The .lib section tells exec what static shared
libraries are needed. The a.out is probably cor‐
rupted.
86 ELIBMAX Attempting to link in more shared libraries than
system limit
Trying to exec an a.out that requires more
static shared libraries than is allowed on the
current configuration of the system. See
87 ELIBEXEC Cannot exec a shared library directly
Attempting to exec a shared library directly.
88 EILSEQ Error 88
Illegal byte sequence. Handle multiple charac‐
ters as a single character.
89 ENOSYS Operation not applicable
90 ELOOP Number of symbolic links encountered during path
name traversal exceeds MAXSYMLINKS
91 ESTART Restartable system call
Interrupted system call should be restarted.
92 ESTRPIPE If pipe/FIFO, don't sleep in stream head
Streams pipe error (not externally visible).
93 ENOTEMPTY Directory not empty
94 EUSERS Too many users
95 ENOTSOCK Socket operation on non-socket
96 EDESTADDRREQ Destination address required
A required address was omitted from an operation
on a transport endpoint. Destination address
required.
97 EMGSIZE Message too long
A message sent on a transport provider was
larger than the internal message buffer or some
other network limit.
98 EPROTOTYPE Protocol wrong type for socket
A protocol was specified that does not support
the semantics of the socket type requested.
99 ENOPROTOOPT Protocol not available
A bad option or level was specified when getting
or setting options for a protocol.
120 EPROTONOSUPPORT Protocol not supported
The protocol has not been configured into the
system or no implementation for it exists.
121 ESOCKTNOSUPPORT Socket type not supported
The support for the socket type has not been
configured into the system or no implementation
for it exists.
122 EOPNOTSUPP Operation not supported on transport endpoint
For example, trying to accept a connection on a
datagram transport endpoint.
123 EPFNOSUPPORT Protocol family not supported
The protocol family has not been configured into
the system or no implementation for it exists.
Used for the Internet protocols.
124 EAFNOSUPPORT Address family not supported by protocol family
An address incompatible with the requested pro‐
tocol was used.
125 EADDRINUSE Address already in use
User attempted to use an address already in use,
and the protocol does not allow this.
126 EADDRNOTAVAIL Cannot assign requested address
Results from an attempt to create a transport
endpoint with an address not on the current
machine.
127 ENETDOWN Network is down
Operation encountered a dead network.
128 ENETUNREACH Network is unreachable
Operation was attempted to an unreachable net‐
work.
129 ENETRESET Network dropped connection because of reset
The host you were connected to crashed and
rebooted.
130 ECONNABORTED Software caused connection abort
A connection abort was caused internal to your
host machine.
131 ECONNRESET Connection reset by peer
A connection was forcibly closed by a peer. This
normally results from a loss of the connection
on the remote host due to a timeout or a reboot.
132 ENOBUFS No buffer space available
An operation on a transport endpoint or pipe was
not performed because the system lacked suffi‐
cient buffer space or because a queue was full.
133 EISCONN Transport endpoint is already connected
A connect request was made on an already con‐
nected transport endpoint; or, a sendto(3SOCKET)
or sendmsg(3SOCKET) request on a connected
transport endpoint specified a destination when
already connected.
134 ENOTCONN Transport endpoint is not connected
A request to send or receive data was disallowed
because the transport endpoint is not connected
and (when sending a datagram) no address was
supplied.
143 ESHUTDOWN Cannot send after transport endpoint shutdown
A request to send data was disallowed because
the transport endpoint has already been shut
down.
144 ETOOMANYREFS Too many references: cannot splice
145 ETIMEDOUT Connection timed out
A connect(3SOCKET) or send(3SOCKET) request
failed because the connected party did not prop‐
erly respond after a period of time; or a
write(2) or fsync(3C) request failed because a
file is on an NFS file system mounted with the
soft option.
146 ECONNREFUSED Connection refused
No connection could be made because the target
machine actively refused it. This usually
results from trying to connect to a service that
is inactive on the remote host.
147 EHOSTDOWN Host is down
A transport provider operation failed because
the destination host was down.
148 EHOSTUNREACH No route to host
A transport provider operation was attempted to
an unreachable host.
149 EALREADY Operation already in progress
An operation was attempted on a non-blocking
object that already had an operation in
progress.
150 EINPROGRESS Operation now in progress
An operation that takes a long time to complete
(such as a connect()) was attempted on a non-
blocking object.
151 ESTALE Stale NFS file handle
DEFINITIONS
Background Process Group
Any process group that is not the foreground process group of a ses‐
sion that has established a connection with a controlling terminal.
Controlling Process
A session leader that established a connection to a controlling termi‐
nal.
Controlling Terminal
A terminal that is associated with a session. Each session may have,
at most, one controlling terminal associated with it and a controlling
terminal may be associated with only one session. Certain input
sequences from the controlling terminal cause signals to be sent to
process groups in the session associated with the controlling terminal;
see termio(7I).
Directory
Directories organize files into a hierarchical system where directories
are the nodes in the hierarchy. A directory is a file that catalogs the
list of files, including directories (sub-directories), that are
directly beneath it in the hierarchy. Entries in a directory file are
called links. A link associates a file identifier with a filename. By
convention, a directory contains at least two links, . (dot) and ..
(dot-dot). The link called dot refers to the directory itself while
dot-dot refers to its parent directory. The root directory, which is
the top-most node of the hierarchy, has itself as its parent directory.
The pathname of the root directory is / and the parent directory of the
root directory is /.
Downstream
In a stream, the direction from stream head to driver.
Driver
In a stream, the driver provides the interface between peripheral hard‐
ware and the stream. A driver can also be a pseudo-driver, such as a
multiplexor or log driver (see log(7D)), which is not associated with a
hardware device.
Effective User ID and Effective Group ID
An active process has an effective user ID and an effective group ID
that are used to determine file access permissions (see below). The
effective user ID and effective group ID are equal to the process's
real user ID and real group ID, respectively, unless the process or one
of its ancestors evolved from a file that had the set-user-ID bit or
set-group-ID bit set (see exec(2)).
File Access Permissions
Read, write, and execute/search permissions for a file are granted to a
process if one or more of the following are true:
o The effective user ID of the process matches the user ID of
the owner of the file and the appropriate access bit of the
"owner" portion (0700) of the file mode is set.
o The effective user ID of the process does not match the
user ID of the owner of the file, but either the effective
group ID or one of the supplementary group IDs of the
process match the group ID of the file and the appropriate
access bit of the "group" portion (0070) of the file mode is
set.
o The effective user ID of the process does not match the user
ID of the owner of the file, and neither the effective group
ID nor any of the supplementary group IDs of the process
match the group ID of the file, but the appropriate access
bit of the "other" portion (0007) of the file mode is set.
o The read, write, or execute mode bit is not set but the
process has the discretionary file access override privilege
for the corresponding mode bit: {PRIV_FILE_DAC_READ} for the
read bit {PRIV_FILE_DAC_WRITE} for the write bit,
{PRIV_FILE_DAC_SEARCH} for the execute bit on directories,
and {PRIV_FILE_DAC_EXECUTE} for the executable bit on plain
files.
Otherwise, the corresponding permissions are denied.
File Descriptor
A file descriptor is a small integer used to perform I/O on a file. The
value of a file descriptor is from 0 to (NOFILES−1). A process may have
no more than NOFILES file descriptors open simultaneously. A file
descriptor is returned by calls such as open(2) or pipe(2). The file
descriptor is used as an argument by calls such as read(2), write(2),
ioctl(2), and close(2).
Each file descriptor has a corresponding offset maximum. For regular
files that were opened without setting the O_LARGEFILE flag, the offset
maximum is 2 Gbyte − 1 byte (2^31 −1 bytes). For regular files that
were opened with the O_LARGEFILE flag set, the offset maximum is 2^63
−1 bytes.
File Name
Names consisting of 1 to NAME_MAX characters may be used to name an
ordinary file, special file or directory.
These characters may be selected from the set of all character values
excluding \0 (null) and the ASCII code for / (slash).
Note that it is generally unwise to use *, ?, [, or ] as part of file
names because of the special meaning attached to these characters by
the shell (see sh(1), csh(1), and ksh(1)). Although permitted, the use
of unprintable characters in file names should be avoided.
A file name is sometimes referred to as a pathname component. The
interpretation of a pathname component is dependent on the values of
NAME_MAX and _POSIX_NO_TRUNC associated with the path prefix of that
component. If any pathname component is longer than NAME_MAX and
_POSIX_NO_TRUNC is in effect for the path prefix of that component (see
fpathconf(2) and limits.h(3HEAD)), it shall be considered an error con‐
dition in that implementation. Otherwise, the implementation shall use
the first NAME_MAX bytes of the pathname component.
Foreground Process Group
Each session that has established a connection with a controlling ter‐
minal will distinguish one process group of the session as the fore‐
ground process group of the controlling terminal. This group has cer‐
tain privileges when accessing its controlling terminal that are denied
to background process groups.
{IOV_MAX}
Maximum number of entries in a struct iovec array.
{LIMIT}
The braces notation, {LIMIT}, is used to denote a magnitude limitation
imposed by the implementation. This indicates a value which may be
defined by a header file (without the braces), or the actual value may
be obtained at runtime by a call to the configuration inquiry path‐
conf(2) with the name argument _PC_LIMIT.
Masks
The file mode creation mask of the process used during any create func‐
tion calls to turn off permission bits in the mode argument supplied.
Bit positions that are set in umask(cmask) are cleared in the mode of
the created file.
Message
In a stream, one or more blocks of data or information, with associated
STREAMS control structures. Messages can be of several defined types,
which identify the message contents. Messages are the only means of
transferring data and communicating within a stream.
Message Queue
In a stream, a linked list of messages awaiting processing by a module
or driver.
Message Queue Identifier
A message queue identifier (msqid) is a unique positive integer created
by a msgget(2) call. Each msqid has a message queue and a data struc‐
ture associated with it. The data structure is referred to as msqid_ds
and contains the following members:
struct ipc_perm msg_perm;
struct msg *msg_first;
struct msg *msg_last;
ulong_t msg_cbytes;
ulong_t msg_qnum;
ulong_t msg_qbytes;
pid_t msg_lspid;
pid_t msg_lrpid;
time_t msg_stime;
time_t msg_rtime;
time_t msg_ctime;
The following are descriptions of the msqid_ds structure members:
The msg_perm member is an ipc_perm structure that specifies the message
operation permission (see below). This structure includes the following
members:
uid_t cuid; /* creator user id */
gid_t cgid; /* creator group id */
uid_t uid; /* user id */
gid_t gid; /* group id */
mode_t mode; /* r/w permission */
ulong_t seq; /* slot usage sequence # */
key_t key; /* key */
The *msg_first member is a pointer to the first message on the queue.
The *msg_last member is a pointer to the last message on the queue.
The msg_cbytes member is the current number of bytes on the queue.
The msg_qnum member is the number of messages currently on the queue.
The msg_qbytes member is the maximum number of bytes allowed on the
queue.
The msg_lspid member is the process ID of the last process that per‐
formed a msgsnd() operation.
The msg_lrpid member is the process id of the last process that per‐
formed a msgrcv() operation.
The msg_stime member is the time of the last msgsnd() operation.
The msg_rtime member is the time of the last msgrcv() operation.
The msg_ctime member is the time of the last msgctl() operation that
changed a member of the above structure.
Message Operation Permissions
In the msgctl(2), msgget(2), msgrcv(2), and msgsnd(2) function descrip‐
tions, the permission required for an operation is given as {token},
where token is the type of permission needed, interpreted as follows:
00400 READ by user
00200 WRITE by user
00040 READ by group
00020 WRITE by group
00004 READ by others
00002 WRITE by others
Read and write permissions for a msqid are granted to a process if one
or more of the following are true:
o The {PRIV_IPC_DAC_READ} or {PRIV_IPC_DAC_WRITE} privilege is
present in the effective set.
o The effective user ID of the process matches msg_perm.cuid
or msg_perm.uid in the data structure associated with msqid
and the appropriate bit of the "user" portion (0600) of
msg_perm.mode is set.
o Any group ID in the process credentials from the set
(cr_gid, cr_groups) matches msg_perm.cgid or msg_perm.gid
and the appropriate bit of the "group" portion (060) of
msg_perm.mode is set.
o The appropriate bit of the "other" portion (006) of
msg_perm.mode is set."
Otherwise, the corresponding permissions are denied.
Module
A module is an entity containing processing routines for input and out‐
put data. It always exists in the middle of a stream, between the
stream's head and a driver. A module is the STREAMS counterpart to the
commands in a shell pipeline except that a module contains a pair of
functions which allow independent bidirectional (downstream and
upstream) data flow and processing.
Multiplexor
A multiplexor is a driver that allows streams associated with several
user processes to be connected to a single driver, or several drivers
to be connected to a single user process. STREAMS does not provide a
general multiplexing driver, but does provide the facilities for con‐
structing them and for connecting multiplexed configurations of
streams.
Offset Maximum
An offset maximum is an attribute of an open file description repre‐
senting the largest value that can be used as a file offset.
Orphaned Process Group
A process group in which the parent of every member in the group is
either itself a member of the group, or is not a member of the process
group's session.
Path Name
A path name is a null-terminated character string starting with an
optional slash (/), followed by zero or more directory names separated
by slashes, optionally followed by a file name.
If a path name begins with a slash, the path search begins at the root
directory. Otherwise, the search begins from the current working direc‐
tory.
A slash by itself names the root directory.
Unless specifically stated otherwise, the null path name is treated as
if it named a non-existent file.
Privileged User
Solaris software implements a set of privileges that provide fine-
grained control over the actions of processes. The possession of of a
certain privilege allows a process to perform a specific set of
restricted operations. Prior to the Solaris 10 release, a process run‐
ning with uid 0 was granted all privileges. See privileges(5) for the
semantics and the degree of backward compatibility awarded to processes
with an effective uid of 0.
Process ID
Each process in the system is uniquely identified during its lifetime
by a positive integer called a process ID. A process ID cannot be
reused by the system until the process lifetime, process group life‐
time, and session lifetime ends for any process ID, process group ID,
and session ID equal to that process ID. There are threads within a
process with thread IDs thread_t and LWPID_t. These threads are not
visible to the outside process.
Parent Process ID
A new process is created by a currently active process (see fork(2)).
The parent process ID of a process is the process ID of its creator.
Privilege
Having appropriate privilege means having the capability to override
system restrictions.
Process Group
Each process in the system is a member of a process group that is iden‐
tified by a process group ID. Any process that is not a process group
leader may create a new process group and become its leader. Any
process that is not a process group leader may join an existing
process group that shares the same session as the process. A newly
created process joins the process group of its parent.
Process Group Leader
A process group leader is a process whose process ID is the same as its
process group ID.
Process Group ID
Each active process is a member of a process group and is identified by
a positive integer called the process group ID. This ID is the process
ID of the group leader. This grouping permits the signaling of related
processes (see kill(2)).
Process Lifetime
A process lifetime begins when the process is forked and ends after it
exits, when its termination has been acknowledged by its parent
process. See wait(3C).
Process Group Lifetime
A process group lifetime begins when the process group is created by
its process group leader, and ends when the lifetime of the last
process in the group ends or when the last process in the group leaves
the group.
Processor Set ID
The processors in a system may be divided into subsets, known as pro‐
cessor sets. A process bound to one of these sets will run only on pro‐
cessors in that set, and the processors in the set will normally run
only processes that have been bound to the set. Each active processor
set is identified by a positive integer. See pset_create(2).
Read Queue
In a stream, the message queue in a module or driver containing mes‐
sages moving upstream.
Real User ID and Real Group ID
Each user allowed on the system is identified by a positive integer (0
to MAXUID) called a real user ID.
Each user is also a member of a group. The group is identified by a
positive integer called the real group ID.
An active process has a real user ID and real group ID that are set to
the real user ID and real group ID, respectively, of the user responsi‐
ble for the creation of the process.
Root Directory and Current Working Directory
Each process has associated with it a concept of a root directory and a
current working directory for the purpose of resolving path name
searches. The root directory of a process need not be the root direc‐
tory of the root file system.
Saved Resource Limits
Saved resource limits is an attribute of a process that provides some
flexibility in the handling of unrepresentable resource limits, as
described in the exec family of functions and setrlimit(2).
Saved User ID and Saved Group ID
The saved user ID and saved group ID are the values of the effective
user ID and effective group ID just after an exec of a file whose set
user or set group file mode bit has been set (see exec(2)).
Semaphore Identifier
A semaphore identifier (semid) is a unique positive integer created by
a semget(2) call. Each semid has a set of semaphores and a data struc‐
ture associated with it. The data structure is referred to as semid_ds
and contains the following members:
struct ipc_perm sem_perm; /* operation permission struct */
struct sem *sem_base; /* ptr to first semaphore in set */
ushort_t sem_nsems; /* number of sems in set */
time_t sem_otime; /* last operation time */
time_t sem_ctime; /* last change time */
/* Times measured in secs since */
/* 00:00:00 GMT, Jan. 1, 1970 */
The following are descriptions of the semid_ds structure members:
The sem_perm member is an ipc_perm structure that specifies the sema‐
phore operation permission (see below). This structure includes the
following members:
uid_t uid; /* user id */
gid_t gid; /* group id */
uid_t cuid; /* creator user id */
gid_t cgid; /* creator group id */
mode_t mode; /* r/a permission */
ulong_t seq; /* slot usage sequence number */
key_t key; /* key */
The sem_nsems member is equal to the number of semaphores in the set.
Each semaphore in the set is referenced by a nonnegative integer
referred to as a sem_num. sem_num values run sequentially from 0 to the
value of sem_nsems minus 1.
The sem_otime member is the time of the last semop(2) operation.
The sem_ctime member is the time of the last semctl(2) operation that
changed a member of the above structure.
A semaphore is a data structure called sem that contains the following
members:
ushort_t semval; /* semaphore value */
pid_t sempid; /* pid of last operation */
ushort_t semncnt; /* # awaiting semval > cval */
ushort_t semzcnt; /* # awaiting semval = 0 */
The following are descriptions of the sem structure members:
The semval member is a non-negative integer that is the actual value of
the semaphore.
The sempid member is equal to the process ID of the last process that
performed a semaphore operation on this semaphore.
The semncnt member is a count of the number of processes that are cur‐
rently suspended awaiting this semaphore's semval to become greater
than its current value.
The semzcnt member is a count of the number of processes that are cur‐
rently suspended awaiting this semaphore's semval to become 0.
Semaphore Operation Permissions
In the semop(2) and semctl(2) function descriptions, the permission
required for an operation is given as {token}, where token is the type
of permission needed interpreted as follows:
00400 READ by user
00200 ALTER by user
00040 READ by group
00020 ALTER by group
00004 READ by others
00002 ALTER by others
Read and alter permissions for a semid are granted to a process if one
or more of the following are true:
o The {PRIV_IPC_DAC_READ} or {PRIV_IPC_DAC_WRITE} privilege is
present in the effective set.
o The effective user ID of the process matches sem_perm.cuid
or sem_perm.uid in the data structure associated with semid
and the appropriate bit of the "user" portion (0600) of
sem_perm.mode is set.
o The effective group ID of the process matches sem_perm.cgid
or sem_perm.gid and the appropriate bit of the "group" por‐
tion (060) of sem_perm.mode is set.
o The appropriate bit of the "other" portion (06) of
sem_perm.mode is set.
Otherwise, the corresponding permissions are denied.
Session
A session is a group of processes identified by a common ID called a
session ID, capable of establishing a connection with a controlling
terminal. Any process that is not a process group leader may create a
new session and process group, becoming the session leader of the ses‐
sion and process group leader of the process group. A newly created
process joins the session of its creator.
Session ID
Each session in the system is uniquely identified during its lifetime
by a positive integer called a session ID, the process ID of its ses‐
sion leader.
Session Leader
A session leader is a process whose session ID is the same as its
process and process group ID.
Session Lifetime
A session lifetime begins when the session is created by its session
leader, and ends when the lifetime of the last process that is a member
of the session ends, or when the last process that is a member in the
session leaves the session.
Shared Memory Identifier
A shared memory identifier (shmid) is a unique positive integer created
by a shmget(2) call. Each shmid has a segment of memory (referred to as
a shared memory segment) and a data structure associated with it. (Note
that these shared memory segments must be explicitly removed by the
user after the last reference to them is removed.) The data structure
is referred to as shmid_ds and contains the following members:
struct ipc_perm shm_perm; /* operation permission struct */
size_t shm_segsz; /* size of segment */
struct anon_map *shm_amp; /* ptr to region structure */
char pad[4]; /* for swap compatibility */
pid_t shm_lpid; /* pid of last operation */
pid_t shm_cpid; /* creator pid */
shmatt_t shm_nattch; /* number of current attaches */
ulong_t shm_cnattch; /* used only for shminfo */
time_t shm_atime; /* last attach time */
time_t shm_dtime; /* last detach time */
time_t shm_ctime; /* last change time */
/* Times measured in secs since */
/* 00:00:00 GMT, Jan. 1, 1970 */
The following are descriptions of the shmid_ds structure members:
The shm_perm member is an ipc_perm structure that specifies the shared
memory operation permission (see below). This structure includes the
following members:
uid_t cuid; /* creator user id */
gid_t cgid; /* creator group id */
uid_t uid; /* user id */
gid_t gid; /* group id */
mode_t mode; /* r/w permission */
ulong_t seq; /* slot usage sequence # */
key_t key; /* key */
The shm_segsz member specifies the size of the shared memory segment in
bytes.
The shm_cpid member is the process ID of the process that created the
shared memory identifier.
The shm_lpid member is the process ID of the last process that per‐
formed a shmat() or shmdt() operation (see shmop(2)).
The shm_nattch member is the number of processes that currently have
this segment attached.
The shm_atime member is the time of the last shmat() operation (see
shmop(2)).
The shm_dtime member is the time of the last shmdt() operation (see
shmop(2)).
The shm_ctime member is the time of the last shmctl(2) operation that
changed one of the members of the above structure.
Shared Memory Operation Permissions
In the shmctl(2), shmat(), and shmdt() (see shmop(2)) function descrip‐
tions, the permission required for an operation is given as {token},
where token is the type of permission needed interpreted as follows:
00400 READ by user
00200 WRITE by user
00040 READ by group
00020 WRITE by group
00004 READ by others
00002 WRITE by others
Read and write permissions for a shmid are granted to a process if one
or more of the following are true:
o The {PRIV_IPC_DAC_READ} or {PRIV_IPC_DAC_WRITE} privilege is
present in the effective set.
o The effective user ID of the process matches shm_perm.cuid
or shm_perm.uid in the data structure associated with shmid
and the appropriate bit of the "user" portion (0600) of
shm_perm.mode is set.
o The effective group ID of the process matches shm_perm.cgid
or shm_perm.gid and the appropriate bit of the "group" por‐
tion (060) of shm_perm.mode is set.
o The appropriate bit of the "other" portion (06) of
shm_perm.mode is set.
Otherwise, the corresponding permissions are denied.
Special Processes
The process with ID 0 and the process with ID 1 are special processes
referred to as proc0 and proc1; see kill(2). proc0 is the process
scheduler. proc1 is the initialization process (init); proc1 is the
ancestor of every other process in the system and is used to control
the process structure.
STREAMS
A set of kernel mechanisms that support the development of network ser‐
vices and data communication drivers. It defines interface standards
for character input/output within the kernel and between the kernel and
user level processes. The STREAMS mechanism is composed of utility rou‐
tines, kernel facilities and a set of data structures.
Stream
A stream is a full-duplex data path within the kernel between a user
process and driver routines. The primary components are a stream head,
a driver, and zero or more modules between the stream head and driver.
A stream is analogous to a shell pipeline, except that data flow and
processing are bidirectional.
Stream Head
In a stream, the stream head is the end of the stream that provides the
interface between the stream and a user process. The principal func‐
tions of the stream head are processing STREAMS-related system calls
and passing data and information between a user process and the stream.
Upstream
In a stream, the direction from driver to stream head.
Write Queue
In a stream, the message queue in a module or driver containing mes‐
sages moving downstream.
SEE ALSOstandards(5), threads(5)SunOS 5.10 4 Oct 2005 Intro(2)
