term% ls -F
term% cat index.txt
ERRSTR(2)                     System Calls Manual                    ERRSTR(2)

       errstr, rerrstr, werrstr - description of last system call error

       #include <u.h>
       #include <libc.h>

       int errstr(char *err, uint nerr)

       void rerrstr(char *err, uint nerr)

       void werrstr(char *fmt, ...)

       When  a  system  call fails it returns -1 and records a null terminated
       string describing the error in a per-process buffer.  Errstr swaps  the
       contents  of  that  buffer  with the contents of the array err.  Errstr
       will write at most nerr bytes into err; if the per-process error string
       does  not  fit,  it  is silently truncated at a UTF character boundary.
       The returned string is NUL-terminated.  Usually errstr will  be  called
       with  an  empty  string, but the exchange property provides a mechanism
       for libraries to set the return value for the next call to errstr.

       The per-process buffer is ERRMAX bytes long.  Any error string provided
       by  the user will be truncated at ERRMAX-1 bytes.  ERRMAX is defined in

       If no system call has generated an error since the last call to  errstr
       with an empty string, the result is an empty string.

       The verb r in print(2) calls errstr and outputs the error string.

       Rerrstr reads the error string but does not modify the per-process buf‐
       fer, so a subsequent errstr will recover the same string.

       Werrstr takes a print style format as its argument and uses it to  for‐
       mat  a  string  to  pass to errstr.  The string returned from errstr is


       Errstr always returns 0.

       intro(2), perror(2)