INTRO(II)                    11/5/73                    INTRO(II)


Section II of this manual lists all the entries into the  system.

In  most  cases two calling sequences are specified, one of which

is usable from assembly language, and the other from C.  Most  of

these  calls  have  an  error  return.  From assembly language an

erroneous call is always indicated by turning on the c-bit of the

condition  codes.  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.

From  C,  an  error  condition  is  indicated  by  an   otherwise

impossible  returned  value.   Almost  always  this  is  -1;  the

individual sections specify the details.

In both cases an error number is  also  available.   In  assembly

language, this number is returned in r0 on erroneous calls.  From

C, the external variable errno is set to the error number.  Errno

is  not  cleared on successful calls, so it should be tested only

after an error has  occurred.   There  is  a  table  of  messages

associated  with  each  error,  and  a  routine  for printing the

message.  See perror (III).

The possible error numbers are not recited with each  writeup  in

section II, since many errors are possible for most of the calls.

Here is a list of the  error  numbers,  their  names  inside  the

system  (for  the  benefit  of  system-readers), and the messages

available using perror.  A short explanation is also provided.

0       -       (unused)

1       EPERM   Not owner and not super-user

   Typically this error indicates an attempt to modify a file  in

   some  way  forbidden except to its owner.  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 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


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  which  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 512 bytes (counting the  null  at

   the end of each argument) 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 one of the magic

   numbers 407 or 410.

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 which 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  and  no  more

   processes can for the moment be created.

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 is such as  to  require  more  than  the  existing  8

   segmentation registers.

13      EACCES  Permission denied

   An attempt was made to access a file in a way forbidden by the

   protection system.

14      -       (unused)

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

   open file or some process's current directory.

17      EEXIST  File exists

   An existing file was mentioned in  an  inappropriate  context,

   e.g.  link.

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: currently,  dismounting  a  non-mounted

   device,  mentioning an unknown signal in signal, and giving an

   unknown request in stty to the TIU special file.

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

   Only 15 files can be open per process.

25      ENOTTY  Not a typewriter

   The file mentioned in stty or gtty is not a typewriter or  one

   of the other devices to which these calls apply.

26      ETXTBSY Text file busy

   An attempt  to  execute  a  pure-procedure  program  which  is

   currently  open for writing (or reading!).  Also an attempt to

   open for  writing  a  pure-procedure  program  that  is  being


27      EFBIG   File too large

   An attempt to make a file larger than  the  maximum  of  32768


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  Seek on pipe

   A seek 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 127 links to a file.

32      EPIPE   Write on 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.