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.TH PERROR 2
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.SH NAME
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perror, syslog, sysfatal \- system error messages
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.B
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void perror(char *s)
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.PP
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.B
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void syslog(int cons, char *logname, char *fmt, ...)
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.PP
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.B
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void sysfatal(char *fmt, ...)
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.SH DESCRIPTION
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.I Perror
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produces a short error message
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on the standard error file
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describing the last error encountered during a call
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to the system.
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First the argument string
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.I s
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is printed, then a colon, then the message and a newline.
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If
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.I s
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is nil, only the error message and newline are printed.
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.PP
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.I Syslog
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logs messages in the file named by
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.I logname
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in the directory
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.BR /sys/log ;
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the file must already exist and should be append-only.
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.I Logname
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must contain no slashes.
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The message is a line with several fields:
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the name of the machine writing the message;
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the date and time;
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the message specified by the
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.IR print (2)
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format
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.I fmt
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and any following arguments;
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and a final newline.
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If
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.I cons
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is set or the log file cannot be opened, the message is also printed
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on the system console.
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.I Syslog
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can be used safely in multi-threaded programs.
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.PP
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.I Sysfatal
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prints to standard error the name of the running program,
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a colon and a space,
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the message described by the
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.IR print (2)
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format string
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.I fmt
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and subsequent arguments, and a newline.
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It then calls
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.IR exits (2)
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with the formatted message as argument.
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The program's name is the value of
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.BR argv0 ,
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which will be set if the program uses the
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.IR arg (2)
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interface to process its arguments.
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If
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.B argv0
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is null, it is ignored and the following colon and space are suppressed.
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.SH SOURCE
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.B /sys/src/libc/port/perror.c
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.br
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.B /sys/src/libc/9sys/syslog.c
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.br
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.B /sys/src/libc/9sys/sysfatal.c
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.SH "SEE ALSO"
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.IR intro (2),
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.IR errstr (2),
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the
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.B %r
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format in
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.IR print (2)
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.SH BUGS
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.I Perror
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is a holdover; the
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.B %r
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format in
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.IR print (2)
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is preferred.