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NAME    [Toc]    [Back]

     intro - introduction to system calls and error numbers

SYNOPSIS    [Toc]    [Back]

     #include <errno.h>

DESCRIPTION    [Toc]    [Back]

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

DIAGNOSTICS    [Toc]    [Back]

     Nearly all of the system calls provide an  error  number  in
the external
     variable errno, which is currently defined as:

           extern int errno;

     Portable  applications  must  not depend on this definition,
and should only
     use errno as defined in <errno.h>.  When a system  call  detects an error,
     it  returns an integer value indicating 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 until 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 Error 0.  Not used.

     1  EPERM  Operation  not  permitted.  An attempt was made to
perform an operation
 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 corresponding to that
             specified by the given process ID.

     4 EINTR Interrupted function call.  An  asynchronous  signal
(such as
             SIGINT  or SIGQUIT) was caught by the process 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 (over written) by any
             subsequent errors.

     6  ENXIO  No  such  device or address.  Input or output on a
special file referred
 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 Arg list too long.  The number of bytes used for the
argument and
             environment list of the  new  process  exceeded  the
limit NCARGS
             (specified in <sys/param.h>).

     8  ENOEXEC Exec format error.  A request was made to execute
a file that,
             although it has the appropriate permissions, was not
in the format
 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 executed
 by a process that had no existing or unwaitedfor child

     11 EDEADLK Resource deadlock avoided.  An attempt  was  made
to lock a system
  resource that would have resulted in a deadlock

     12 ENOMEM Cannot allocate memory.  The new process image required more
             memory  than  was allowed by the hardware or by system-imposed memory
 management constraints.  A lack of swap space is
             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 attempting
 to use an argument of a call.

     15 ENOTBLK Not a block device.  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
 context, for instance, as the new link name in a

     18  EXDEV  Improper  link.  A hard link to a file on another
file system was

     19 ENODEV Operation not supported by device.  An attempt was
made to apply
 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 existed,
 but it was not a directory, when a directory was

     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 descriptors
 allowable on the system has been reached and  a
request for
             an  open  cannot be satisfied until at least one has
been closed.

     24 EMFILE Too many open files.  (As released, the  limit  on
the number of
             open  files  per  process  is 64.)  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.  The new process was a pure  procedure (shared
             text)  file  which  was  open for writing by another
process, or
             while the pure procedure file was being executed  an
open(2) call
             requested write access.

     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

     28 ENOSPC Device out of space.  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 readonly at the

     31 EMLINK Too many links.  Maximum allowable hard links to a
single file
             has  been  exceeded  (limit  of 32767 hard links per

     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 out of range.  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 condition
 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 nonblocking
 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

     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 Protocol not available.  A bad option or level was specified
 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
             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 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

     47  EAFNOSUPPORT  Address  family  not supported by protocol
family.  An address
 incompatible with the requested  protocol  was
used.  For example,
  you  shouldn't necessarily expect to be able
to use NS addresses
 with ARPA Internet protocols.

     48 EADDRINUSE Address already in use.   Only  one  usage  of
each address is
             normally permitted.

     49  EADDRNOTAVAIL Cannot 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 a loss of the
             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) request
  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  Cannot 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 period
 of time.  (The timeout period is  dependent  on
the communication

     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

     62 ELOOP Too many levels of symbolic  links.   A  path  name
lookup involved
             more than 32 symbolic links.

     63  ENAMETOOLONG  File name too long.  A component of a path
name exceeded
             255 (MAXNAMELEN) characters, or an entire path  name
exceeded 1023
             (MAXPATHLEN-1) characters.

     64  EHOSTDOWN  Host  is down.  A socket operation failed because the destination
 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

     69 EDQUOT Disc quota exceeded.  A write(2)  to  an  ordinary
file, the creation
  of  a directory or symbolic link, or the creation of a directory
 entry failed because  the  user's  quota  of
disk blocks was
             exhausted, or the allocation of an inode for a newly
created file
             failed because the user's quota of  inodes  was  exhausted.

     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 information
was unsuccessful.

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

     74  EPROGUNAVAIL RPC prog. not avail.  The requested program
is not registered
 on the remote host.

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

     76  EPROCUNAVAIL Bad procedure for program.  An RPC 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
 ticket to mount a NFS filesystem.

     81  ENEEDAUTH  Need authenticator.  An authentication ticket
must be obtained
 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.

DEFINITIONS    [Toc]    [Back]

     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 1 to 32766.

     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,

     Process Group
             Each  active  process is a member of a process group
that is identified
 by a non-negative integer called the  process
group ID.
             This  is  the  process ID of the group leader.  This
grouping permits
  the  signaling  of  related   processes   (see
termios(4)) and the
             job control mechanisms of 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

     Controlling Process
             A  session  leader  with a controlling terminal is a

     Controlling Terminal
             A terminal that is  associated  with  a  session  is
known as the controlling
  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
csh(1) and

     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.

     Real User ID and Real Group ID
             Each  user on the system is identified by a positive
             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.

     Effective User ID, Effective Group ID, and Group Access List
             Access to system resources is governed by  two  values: the effective
  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 supplementary
 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-groupID
 file (possibly by one  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-groupID
 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 determining
  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 effective
 group ID (first element of the group  access
list) is set
             to  the  group of the file if the file is set-groupID.  The effective
 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 setgid,
 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, 1,  and  2  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 system.
   It  is used to control the process structure.
Process 2 is
             the paging daemon.

             An integer assigned by the system  when  a  file  is
referenced by
             open(2)  or  dup(2),  or when a socket is created by
             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  (MAXNAMELEN)  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 (NUL) and the ASCII code for `/'

             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 (MAXNAMELEN) 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
             pathconf(2) and fpathconf(2).

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

             If  a path name begins with a slash, the path search
begins at the
             root directory.  Otherwise, the search  begins  from
the current
             working directory.  A slash by itself names the root
             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
             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
             should be granted by checking the access information
             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

             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

             Otherwise, permission is denied.

     Sockets and Address Families

             A socket is an endpoint  for  communication  between
             Each socket has queues for sending and receiving data.

             Sockets are typed according to their  communications
             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.

SEE ALSO    [Toc]    [Back]

     intro(3), perror(3)

HISTORY    [Toc]    [Back]

     An intro manual page appeared in Version 6 AT&T UNIX.

OpenBSD      3.6                        December     11,     1993
[ Back ]
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