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INTRO(2)                      System Calls Manual                     INTRO(2)

       intro, errno - introduction to system calls and error numbers

       #include <&lt;errno.h>&gt;

       Section  2  of this manual lists all the entries into the system.  Most
       of these calls have an error return.  An error condition  is  indicated
       by  an  otherwise impossible returned value.  Almost always this is -1;
       the individual sections specify the details.  An error number  is  also
       made available in the external variable errno.  Errno is not cleared on
       successful calls, so it should  be  tested  only  after  an  error  has

       There  is a table of messages associated with each error, and a routine
       for printing the message; See perror(3).  The  possible  error  numbers
       are  not  recited with each writeup in section 2, since many errors are
       possible for most of the calls.  Here is a list of the  error  numbers,
       their  names  as defined in <errno.h>, and the messages available using

       0       Error 0

       1  EPERM  Not owner
              Typically this error indicates an attempt to modify  a  file  in
              some  way  forbidden  except  to its owner or super-user.  It is
              also returned for  attempts  by  ordinary  users  to  do  things
              allowed only to the super-user.

       2  ENOENT  No such file or directory
              This  error  occurs  when  a file name is specified and the file
              should exist but doesn't, or when one of the  directories  in  a
              path name does not exist.

       3  ESRCH  No such process
              The process whose number was given to signal and ptrace does not
              exist, or is already dead.

       4  EINTR  Interrupted system call
              An asynchronous signal (such as interrupt or  quit),  which  the
              user  has  elected  to catch, occurred during a system call.  If
              execution is resumed after processing the signal, it will appear
              as if the interrupted system call returned this error condition.

       5  EIO  I/O error
              Some  physical  I/O error occurred during a read or write.  This
              error may in some cases occur on a call  following  the  one  to
              which it actually applies.

       6  ENXIO  No such device or address
              I/O on a special file refers to a subdevice that does not exist,
              or beyond the limits of the device.  It may also occur when, for
              example,  a  tape  drive  is  not  dialled in or no disk pack is
              loaded on a drive.

       7  E2BIG  Arg list too long
              An argument list longer than 5120 bytes is presented to exec.

       8  ENOEXEC  Exec format error
              A request is made to execute a file which, although it  has  the
              appropriate  permissions, does not start with a valid magic num-
              ber, see a.out(5).

       9  EBADF  Bad file number
              Either a file descriptor refers to  no  open  file,  or  a  read
              (resp.  write)  request  is made to a file that is open only for
              writing (resp. reading).

       10  ECHILD  No children
              Wait and the process has no living or unwaited-for children.

       11  EAGAIN  No more processes
              In a fork, the system's process table is full or the user is not
              allowed to create any more processes.

       12  ENOMEM  Not enough core
              During  an  exec or break, a program asks for more core than the
              system is able to supply.  This is not  a  temporary  condition;
              the maximum core size is a system parameter.  The error may also
              occur if the arrangement  of  text,  data,  and  stack  segments
              requires too many segmentation registers.

       13  EACCES  Permission denied
              An  attempt  was made to access a file in a way forbidden by the
              protection system.

       14  EFAULT  Bad address
              The system encountered a hardware fault in attempting to  access
              the arguments of a system call.

       15  ENOTBLK  Block device required
              A  plain  file  was mentioned where a block device was required,
              e.g. in mount.

       16  EBUSY  Mount device busy
              An attempt to mount a device that  was  already  mounted  or  an
              attempt  was  made  to  dismount  a  device on which there is an
              active file (open  file,  current  directory,  mounted-on  file,
              active text segment).

       17  EEXIST  File exists
              An existing file was mentioned in an inappropriate context, e.g.

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

       19  ENODEV  No such device
              An attempt was made to apply an inappropriate system call  to  a
              device; e.g. 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 name or as an argument to chdir.

       21  EISDIR  Is a directory
              An attempt to write on a directory.

       22  EINVAL  Invalid argument
              Some invalid argument: dismounting a  non-mounted  device,  men-
              tioning  an  unknown signal in signal, reading or writing a file
              for which seek has generated a negative pointer.   Also  set  by
              math functions, see intro(3).

       23  ENFILE  File table overflow
              The  system's  table  of  open files is full, and temporarily no
              more opens can be accepted.

       24  EMFILE  Too many open files
              Customary configuration limit is 20 per process.

       25  ENOTTY  Not a typewriter
              The file mentioned in stty or gtty is not a terminal or  one  of
              the other devices to which these calls apply.

       26  ETXTBSY  Text file busy
              An attempt to execute a pure-procedure program that is currently
              open for writing (or reading!).  Also an  attempt  to  open  for
              writing a pure-procedure program that is being executed.

       27  EFBIG  File too large
              The size of a file exceeded the maximum (about 1.0E9 bytes).

       28  ENOSPC  No space left on device
              During  a write to an ordinary file, there is no free space left
              on the device.

       29  ESPIPE  Illegal seek
              An lseek was issued to a pipe.  This error should also be issued
              for other non-seekable devices.

       30  EROFS  Read-only file system
              An  attempt  to  modify a file or directory was made on a device
              mounted read-only.

       31  EMLINK  Too many links
              An attempt to make more than 32767 links to a file.

       32  EPIPE  Broken pipe
              A write on a pipe for which there is  no  process  to  read  the
              data.   This condition normally generates a signal; the error is
              returned if the signal is ignored.

       33  EDOM  Math argument
              The argument of a function in the math package (3M)  is  out  of
              the domain of the function.

       34  ERANGE  Result too large
              The  value  of  a  function in the math package (3M) is unrepre-
              sentable within machine precision.


       as /usr/include/sys.s file ...

       The PDP11 assembly language interface is given for  each  system  call.
       The assembler symbols are defined in `/usr/include/sys.s'.

       Return  values  appear in registers r0 and r1; it is unwise to count on
       these registers being preserved when no value is  expected.   An  erro-
       neous call is always indicated by turning on the c-bit of the condition
       codes.  The error number is returned in r0.  The presence of  an  error
       is most easily tested by the instructions bes and bec (`branch on error
       set (or clear)').  These are synonyms for the bcs and bcc instructions.

       On the Interdata 8/32, the system call arguments correspond well to the
       arguments of the C routines.  The sequence is:

              la   %2,errno
              l    %0,&callno
              svc  0,args

       Thus  register  2  points to a word into which the error number will be
       stored as needed; it is cleared if no error occurs.   Register  0  con-
       tains  the system call number; the nomenclature is identical to that on
       the PDP11.  The argument of the svc is the address  of  the  arguments,
       laid  out in storage as in the C calling sequence.  The return value is
       in register 2 (possibly 3 also, as in pipe) and is -1 in case of error.
       The  overflow  bit  in  the program status word is also set when errors