Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
INTRO(2)		  FreeBSD System Calls Manual		      INTRO(2)

     intro, errno -- introduction to system calls and error numbers

     #include <errno.h>

     The manual	pages in section 2 provide an overview of the system calls,
     their error returns, and other common definitions and concepts.

     Programs may be restricted	to a subset of system calls with pledge(2).

     Nearly all	of the system calls provide an error number via	the identifier
     errno, which expands to an	addressable location of	type int.  The address
     of	errno in each thread is	guaranteed to be unique	for the	lifetime of
     the thread.  Applications must use	errno as defined in <errno.h> and not
     attempt to	use a custom definition.

     When a system call	detects	an error, it returns an	integer	value indicat-
     ing failure (usually -1) and sets the variable errno accordingly.	(This
     allows interpretation of the failure on receiving a -1 and	to take	action
     accordingly.)  Successful calls never set errno; once set,	it remains un-
     til another error occurs.	It should only be examined after an error.
     Note that a number	of system calls	overload the meanings of these error
     numbers, and that the meanings must be interpreted	according to the type
     and circumstances of the call.

     The following is a	complete list of the errors and	their names as given
     in	<sys/errno.h>.

     0 Undefined error:	0.  Not	used.

     1 EPERM Operation not permitted.  An attempt was made to perform an oper-
	     ation limited to processes	with appropriate privileges or to the
	     owner of a	file or	other resources.

     2 ENOENT No such file or directory.  A component of a specified pathname
	     did not exist, or the pathname was	an empty string.

     3 ESRCH No	such process.  No process could	be found which corresponds to
	     the given process ID.

     4 EINTR Interrupted system	call.  An asynchronous signal (such as SIGINT
	     or	SIGQUIT) was caught by the thread during the execution of an
	     interruptible function.  If the signal handler performs a normal
	     return, the interrupted function call will	seem to	have returned
	     the error condition.

     5 EIO Input/output	error.	Some physical input or output error occurred.
	     This error	will not be reported until a subsequent	operation on
	     the same file descriptor and may be lost (overwritten) by any
	     subsequent	errors.

     6 ENXIO Device not	configured.  Input or output on	a special file re-
	     ferred to a device	that did not exist, or made a request beyond
	     the limits	of the device.	This error may also occur when,	for
	     example, a	tape drive is not online or no disk pack is loaded on
	     a drive.

     7 E2BIG Argument list too long.  The number of bytes used for the argu-
	     ment and environment list of the new process exceeded the limit

     8 ENOEXEC Exec format error.  A request was made to execute a file	that,
	     although it has the appropriate permissions, was not in the for-
	     mat required for an executable file.

     9 EBADF Bad file descriptor.  A file descriptor argument was out of
	     range, referred to	no open	file, or a read	(write)	request	was
	     made to a file that was only open for writing (reading).

     10	ECHILD No child	processes.  A wait(2) or waitpid(2) function was exe-
	     cuted by a	process	that had no existing or	unwaited-for child

     11	EDEADLK	Resource deadlock avoided.  An attempt was made	to lock	a sys-
	     tem resource that would have resulted in a	deadlock situation.

     12	ENOMEM Cannot allocate memory.	The new	process	image required more
	     memory than was allowed by	the hardware or	by system-imposed mem-
	     ory management constraints.  A lack of swap space is normally
	     temporary;	however, a lack	of core	is not.	 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 its file access permissions.

     14	EFAULT Bad address.  The system	detected an invalid address in at-
	     tempting to use an	argument of a call.

     15	ENOTBLK	Block device required.	A block	device operation was attempted
	     on	a non-block device or file.

     16	EBUSY Device busy.  An attempt to use a	system resource	which was in
	     use at the	time in	a manner which would have conflicted with the

     17	EEXIST File exists.  An	existing file was mentioned in an inappropri-
	     ate context, for instance,	as the new link	name in	a link(2)

     18	EXDEV Cross-device link.  A hard link to a file	on another file	system
	     was attempted.

     19	ENODEV Operation not supported by device.  An attempt was made to ap-
	     ply an inappropriate function to a	device,	for example, trying to
	     read a write-only device such as a	printer.

     20	ENOTDIR	Not a directory.  A component of the specified pathname	ex-
	     isted, but	it was not a directory,	when a directory was expected.

     21	EISDIR Is a directory.	An attempt was made to open a directory	with
	     write mode	specified.

     22	EINVAL Invalid argument.  Some invalid argument	was supplied.  (For
	     example, specifying an undefined signal to	a signal(3) or kill(2)

     23	ENFILE Too many	open files in system.  Maximum number of file descrip-
	     tors allowable on the system has been reached and a request for
	     an	open cannot be satisfied until at least	one has	been closed.
	     The sysctl(2) variable kern.maxfiles contains the current limit.

     24	EMFILE Too many	open files.  The maximum number	of file	descriptors
	     allowable for this	process	has been reached and a request for an
	     open cannot be satisfied until at least one has been closed.
	     getdtablesize(3) will obtain the current limit.

     25	ENOTTY Inappropriate ioctl for device.	A control function (see
	     ioctl(2)) was attempted for a file	or special device for which
	     the operation was inappropriate.

     26	ETXTBSY	Text file busy.	 An attempt was	made either to execute a pure
	     procedure (shared text) file which	was open for writing by	an-
	     other process, or to open with write access a pure	procedure file
	     that is currently being executed.

     27	EFBIG File too large.  The size	of a file exceeded the maximum.	 (The
	     system-wide maximum file size is 2**63 bytes.  Each file system
	     may impose	a lower	limit for files	contained within it.)

     28	ENOSPC No space	left on	device.	 A write(2) 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	were available
	     on	the file system, or the	allocation of an inode for a newly
	     created file failed because no more inodes	were available on the
	     file system.

     29	ESPIPE Illegal seek.  An lseek(2) function was issued on a socket,
	     pipe or FIFO.

     30	EROFS Read-only	file system.  An attempt was made to modify a file or
	     create a directory	on a file system that was read-only at the

     31	EMLINK Too many	links.	The maximum allowable number of	hard links to
	     a single file has been exceeded (see pathconf(2) for how to ob-
	     tain this value).

     32	EPIPE Broken pipe.  A write on a pipe, socket or FIFO for which	there
	     is	no process to read the data.

     33	EDOM Numerical argument	out of domain.	A numerical input argument was
	     outside the defined domain	of the mathematical function.

     34	ERANGE Result too large.  A result of the function was too large to
	     fit in the	available space	(perhaps exceeded precision).

     35	EAGAIN Resource	temporarily unavailable.  This is a temporary condi-
	     tion and later calls to the same routine may complete normally.

     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 fcntl(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 or some other network limit.

     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 Internet UDP protocol with	type

     42	ENOPROTOOPT Protocol not available.  A bad option or level was speci-
	     fied in a getsockopt(2) or	setsockopt(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.  The attempted operation is	not
	     supported for the type of object referenced.  Usually this	occurs
	     when a file descriptor refers to a	file or	socket that cannot
	     support this operation, for example, trying to accept a connec-
	     tion 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

     47	EAFNOSUPPORT Address family not	supported by protocol family.  An ad-
	     dress incompatible	with the requested protocol was	used.  For ex-
	     ample, you	shouldn't necessarily expect to	be able	to use NS ad-
	     dresses with 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 ma-

     50	ENETDOWN Network is down.  A socket operation encountered a dead net-

     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 con-
	     nected 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 a loss of the connection
	     on	the remote socket due to a timeout or a	reboot.

     55	ENOBUFS	No buffer space	available.  An operation on a socket or	pipe
	     was not performed because the system lacked sufficient buffer
	     space or because a	queue was full.

     56	EISCONN	Socket is already connected.  A	connect(2) request was made on
	     an	already	connected socket; or, a	sendto(2) or sendmsg(2)	re-
	     quest on a	connected socket specified a destination when already

     57	ENOTCONN Socket	is not connected.  A request to	send or	receive	data
	     was disallowed because the	socket was not connected and (when
	     sending on	a datagram socket) no address was supplied.

     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	ETOOMANYREFS Too many references: can't	splice.	 Not used in OpenBSD.

     60	ETIMEDOUT Operation timed out.	A connect(2) or	send(2)	request	failed
	     because the connected party did not properly respond after	a pe-
	     riod of time.  (The timeout period	is dependent on	the communica-
	     tion 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 for-
	     eign host.

     62	ELOOP Too many levels of symbolic links.  A pathname lookup involved
	     more than 32 (SYMLOOP_MAX)	symbolic links.

     63	ENAMETOOLONG File name too long.  A component of a pathname exceeded
	     255 (NAME_MAX) characters,	or an entire pathname (including the
	     terminating NUL) exceeded 1024 (PATH_MAX) bytes.

     64	EHOSTDOWN Host is down.	 A socket operation failed because the desti-
	     nation host was down.

     65	EHOSTUNREACH No	route to host.	A socket operation was attempted to an
	     unreachable host.

     66	ENOTEMPTY Directory not	empty.	A directory with entries other than
	     `.' and `..' was supplied to a remove directory or	rename call.

     67	EPROCLIM Too many processes.

     68	EUSERS Too many	users.	The quota system ran out of table entries.

     69	EDQUOT Disk quota exceeded.  A write(2)	to an ordinary file, the cre-
	     ation of a	directory or symbolic link, or the creation of a di-
	     rectory 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 attempt was made to access an	open
	     file on an	NFS filesystem which is	now unavailable	as referenced
	     by	the file descriptor.  This may indicate	the file was deleted
	     on	the NFS	server or some other catastrophic event	occurred.

     72	EBADRPC	RPC struct is bad.  Exchange of	rpc(3) information was unsuc-

     73	ERPCMISMATCH RPC version wrong.	 The version of	rpc(3) on the remote
	     peer is not compatible with the local version.

     74	EPROGUNAVAIL RPC program not available.	 The requested rpc(3) program
	     is	not registered on the remote host.

     75	EPROGMISMATCH Program version wrong.  The requested version of the
	     rpc(3) program is not available on	the remote host.

     76	EPROCUNAVAIL Bad procedure for program.	 An rpc(3) call	was attempted
	     for a procedure which doesn't exist in the	remote program.

     77	ENOLCK No locks	available.  A system-imposed limit on the number of
	     simultaneous file locks was reached.

     78	ENOSYS Function	not implemented.  Attempted a system call that is not
	     available on this system.

     79	EFTYPE Inappropriate file type or format.  The file contains invalid
	     data or set to invalid modes.

     80	EAUTH Authentication error.  Attempted to use an invalid authentica-
	     tion ticket to mount a NFS	filesystem.

     81	ENEEDAUTH Need authenticator.  An authentication ticket	must be	ob-
	     tained before the given NFS filesystem may	be mounted.

     82	EIPSEC IPsec processing	failure.  IPsec	subsystem error.  Not used in

     83	ENOATTR	Attribute not found.  A	UFS Extended Attribute is not found
	     for the specified pathname.

     84	EILSEQ Illegal byte sequence.  An illegal sequence of bytes was	used
	     when using	wide characters.

     85	ENOMEDIUM No medium found.  Attempted to use a removable media device
	     with no medium present.

     86	EMEDIUMTYPE Wrong medium type.	Attempted to use a removable media de-
	     vice with incorrect or incompatible medium.

     87	EOVERFLOW Value	too large to be	stored in data type.  A	numerical re-
	     sult of the function was too large	to be stored in	the caller
	     provided space.

     88	ECANCELED Operation canceled.  The requested operation was canceled.

     89	EIDRM Identifier removed.  An IPC identifier was removed while the
	     current thread was	waiting	on it.

     90	ENOMSG No message of desired type.  An IPC message queue does not con-
	     tain a message of the desired type, or a message catalog does not
	     contain the requested message.

     91	ENOTSUP	Not supported.	The operation has requested an unsupported

     92	EBADMSG	Bad message.  A	corrupted message was detected.

     93	ENOTRECOVERABLE	State not recoverable.	The state protected by a ro-
	     bust mutex	is not recoverable.

     94	EOWNERDEAD Previous owner died.	 The owner of a	robust mutex termi-
	     nated while holding the mutex lock.

     95	EPROTO Protocol	error.	A device-specific protocol error occurred.

	     A process is a collection of one or more threads, plus the	re-
	     sources shared by those threads such as process ID, address
	     space, user IDs and group IDs, and	root directory and current
	     working directory.

     Process ID
	     Each active process in the	system is uniquely identified by a
	     non-negative integer called a process ID.	The range of this ID
	     is	from 0 to 99999.

     Parent Process ID
	     A new process is created by a currently active process; (see
	     fork(2)).	The parent process ID of a process is initially	the
	     process ID	of its creator.	 If the	creating process exits,	the
	     parent process ID of each child is	set to the ID of a system
	     process, init(8).

     Process Group
	     Each active process is a member of	a process group	that is	iden-
	     tified by a non-negative integer called the process group ID.
	     This is the process ID of the group leader.  This grouping	per-
	     mits the signaling	of related processes (see termios(4)) and the
	     job control mechanisms of ksh(1) and csh(1).

	     A session is a set	of one or more process groups.	A session is
	     created by	a successful call to setsid(2),	which causes the
	     caller to become the only member of the only process group	in the
	     new session.

     Session Leader
	     A process that has	created	a new session by a successful call to
	     setsid(2),	is known as a session leader.  Only a session leader
	     may acquire a terminal as its controlling terminal	(see

     Controlling Process
	     A session leader with a controlling terminal is a controlling

     Controlling Terminal
	     A terminal	that is	associated with	a session is known as the con-
	     trolling terminal for that	session	and its	members.

     Terminal Process Group ID
	     A terminal	may be acquired	by a session leader as its controlling
	     terminal.	Once a terminal	is associated with a session, any of
	     the process groups	within the session may be placed into the
	     foreground	by setting the terminal	process	group ID to the	ID of
	     the process group.	 This facility is used to arbitrate between
	     multiple jobs contending for the same terminal; (see ksh(1),
	     csh(1), and tty(4)).

     Orphaned Process Group
	     A process group is	considered to be orphaned if it	is not under
	     the control of a job control shell.  More precisely, a process
	     group is orphaned when none of its	members	has a parent process
	     that is in	the same session as the	group, but is in a different
	     process group.  Note that when a process exits, the parent
	     process for its children is changed to be init(8),	which is in a
	     separate session.	Not all	members	of an orphaned process group
	     are necessarily orphaned processes	(those whose creating process
	     has exited).  The process group of	a session leader is orphaned
	     by	definition.

     Thread  A thread is a preemptively	scheduled flow of control within a
	     process, with its own set of register values, floating point en-
	     vironment,	thread ID, signal mask,	pending	signal set, alternate
	     signal stack, thread control block	address, resource utilization,
	     errno variable location, and values for thread-specific keys.  A
	     process initially has just	one thread, a duplicate	of the thread
	     in	the parent process that	created	this process.

     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 ac-
	     counting 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.

     Effective User ID,	Effective Group	ID, and	Group Access List
	     Access to system resources	is governed by two values: the effec-
	     tive user ID, and the group access	list.  The first member	of the
	     group access list is also known as	the effective group ID.	 (In
	     POSIX.1, the group	access list is known as	the set	of supplemen-
	     tary group	IDs, and it is unspecified whether the effective group
	     ID	is a member of the 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)).  By
	     convention, the effective group ID	(the first member of the group
	     access list) is duplicated, so that the execution of a set-group-
	     ID	program	does not result	in the loss of the original (real)
	     group ID.

	     The group access list is a	set of group IDs used only in deter-
	     mining resource accessibility.  Access checks are performed as
	     described below in	"File Access Permissions".

     Saved Set User ID and Saved Set Group ID
	     When a process executes a new file, the effective user ID is set
	     to	the owner of the file if the file is set-user-ID, and the ef-
	     fective group ID (first element of	the group access list) is set
	     to	the group of the file if the file is set-group-ID.  The	effec-
	     tive user ID of the process is then recorded as the saved set-
	     user-ID, and the effective	group ID of the	process	is recorded as
	     the saved set-group-ID.  These values may be used to regain those
	     values as the effective user or group ID after reverting to the
	     real ID (see setuid(2)).  (In POSIX.1, the	saved set-user-ID and
	     saved set-group-ID	are optional, and are used in setuid and set-
	     gid, but this does	not work as desired for	the superuser.)

	     A process is recognized as	a superuser process and	is granted
	     special privileges	if its effective user ID is 0.

     Special Processes
	     The processes with	process	IDs of 0 and 1 are special.  Process 0
	     is	the scheduler.	Process	1 is the initialization	process
	     init(8), and is the ancestor of every other process in the	sys-
	     tem.  It is used to control the process structure.

	     An	integer	assigned by the	system when a file is referenced by
	     open(2) or	dup(2),	or when	a socket is created by pipe(2),
	     socket(2) or socketpair(2), which uniquely	identifies an access
	     path to that file or socket from a	given process or any of	its

     File Name
	     Names consisting of up to 255 (NAME_MAX) characters may be	used
	     to	name an	ordinary file, special file, or	directory.

	     These characters may be arbitrary eight-bit values, excluding 0
	     (NUL) 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.

	     Note also that NAME_MAX is	an upper limit fixed by	the kernel,
	     meant to be used for sizing buffers.  Some	filesystems may	have
	     additional	restrictions.  These can be queried using pathconf(2)
	     and fpathconf(2).

	     A pathname	is a NUL-terminated character string starting with an
	     optional slash `/', followed by zero or more directory names sep-
	     arated by slashes,	optionally followed by a file name.  The total
	     length of a pathname must be less than 1024 (PATH_MAX) charac-
	     ters.  Additional restrictions may	apply, depending upon the
	     filesystem, to be queried with pathconf(2)	or fpathconf(2)	if

	     If	a pathname 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.
	     An	empty pathname is invalid.

	     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

     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.

     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 per-
	     mission to	control	if the directory may be	searched.

	     File access permissions are interpreted by	the system as they ap-
	     ply 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 superuser.	(Note:
	     even the superuser	cannot execute a non-executable	file.)

	     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 al-
	     low 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

	     Otherwise,	permission is 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 com-
	     munications 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.

     pledge(2),	intro(3), perror(3)

     An	intro manual for section 2 first appeared in Version 5 AT&T UNIX.

FreeBSD	13.0			January	3, 2021			  FreeBSD 13.0


Want to link to this manual page? Use this URL:

home | help