+.th INTRO II 11/5/73
+.de pg
+.sp
+..
+.de en
+.pg
+.in 3
+.ti 0
+\\$1\t\\$2\t\\$3
+.br
+..
+.sp 2
+.in 0
+.if t .ta 3 10
+.ce
+INTRODUCTION TO SYSTEM CALLS
+.sp
+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
+.it bes
+and
+.it bec
+(``branch on error set (or clear)'').
+These are synonyms for
+the
+.it bcs
+and
+.it bcc
+instructions.
+.pg
+From C, an error condition is indicated by an otherwise
+impossible returned value.
+Almost always this is \(mi1;
+the individual sections specify the details.
+.pg
+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
+.it errno
+is set to the error number.
+.it 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
+.it "perror (III)."
+.pg
+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
+.it perror.
+A short explanation is also provided.
+.en 0 \(mi (unused)
+.en 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.
+.en 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.
+.en 3 ESRCH "No such process"
+The process whose number was given to
+.it signal
+does not exist, or is already dead.
+.en 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.
+.en 5 EIO "I/O error"
+Some physical I/O error occurred during a
+.it read
+or
+.it write.
+This error may in some cases occur
+on a call following the one to which it actually applies.
+.en 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.
+.en 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
+.it exec.
+.en 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.
+.en 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).
+.en 10 ECHILD "No children"
+.it Wait
+and the process has no
+living or unwaited-for children.
+.en 11 EAGAIN "No more processes"
+In a
+.it fork,
+the system's process table is full and no
+more processes can for the moment be created.
+.en 12 ENOMEM "Not enough core"
+During an
+.it exec
+or
+.it 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.
+.en 13 EACCES "Permission denied"
+An attempt was made to access a file in a way forbidden
+by the protection system.
+.en 14 \(mi (unused)
+.en 15 ENOTBLK "Block device required"
+A plain file was mentioned where a block device was required,
+e.g. in
+.it mount.
+.en 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.
+.en 17 EEXIST "File exists"
+An existing file was mentioned in an inappropriate context,
+e.g.
+.it link.
+.en 18 EXDEV "Cross-device link"
+A link to a file on another device
+was attempted.
+.en 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.
+.en 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
+.it chdir.
+.en 21 EISDIR "Is a directory"
+An attempt to write on a directory.
+.en 22 EINVAL "Invalid argument"
+Some invalid argument:
+currently, dismounting a non-mounted
+device,
+mentioning an unknown signal in
+.it signal,
+and giving an unknown request in
+.it stty
+to the TIU special file.
+.en 23 ENFILE "File table overflow"
+The system's table of open files is full,
+and temporarily no more
+.it opens
+can be accepted.
+.en 24 EMFILE "Too many open files"
+Only 15 files can be open per process.
+.en 25 ENOTTY "Not a typewriter"
+The file mentioned in
+.it stty
+or
+.it gtty
+is not a typewriter or one of the other
+devices to which these calls apply.
+.en 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 executed.
+.en 27 EFBIG "File too large"
+An attempt to make a file larger than the maximum of 32768 blocks.
+.en 28 ENOSPC "No space left on device"
+During a
+.it write
+to an ordinary file,
+there is no free space left on the device.
+.en 29 ESPIPE "Seek on pipe"
+A
+.it seek
+was issued to a pipe.
+This error should also be issued for
+other non-seekable devices.
+.en 30 EROFS "Read-only file system"
+An attempt to modify a file or directory
+was made
+on a device mounted read-only.
+.en 31 EMLINK "Too many links"
+An attempt to make more than 127 links to a file.
+.en 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.
projects / unix-history / commitdiff