err,  verr,  errx,  verrx, warn, vwarn, warnx, vwarnx - formatted error


   #include <err.h>

   void err(int eval, const char *fmt, ...);

   void errx(int eval, const char *fmt, ...);

   void warn(const char *fmt, ...);

   void warnx(const char *fmt, ...);

   #include <stdarg.h>

   void verr(int eval, const char *fmt, va_list args);

   void verrx(int eval, const char *fmt, va_list args);

   void vwarn(const char *fmt, va_list args);

   void vwarnx(const char *fmt, va_list args);


   The err() and warn() family of  functions  display  a  formatted  error
   message on the standard error output.  In all cases, the last component
   of the program name, a colon character, and a space are output.  If the
   fmt argument is not NULL, the printf(3)-like formatted error message is
   output.  The output is terminated by a newline character.

   The err(), verr(),  warn(),  and  vwarn()  functions  append  an  error
   message  obtained  from strerror(3) based on the global variable errno,
   preceded by another colon and space unless the fmt argument is NULL.

   The errx() and warnx() functions do not append an error message.

   The err(), verr(), errx(), and verrx() functions  do  not  return,  but
   exit with the value of the argument eval.


   For   an   explanation   of   the  terms  used  in  this  section,  see

   Interface          Attribute      Value          
   err(), errx(),     Thread safety  MT-Safe locale 
   warn(), warnx(),                                 
   verr(), verrx(),                                 
   vwarn(), vwarnx()                                


   These functions are nonstandard BSD extensions.


   Display the current errno information string and exit:

       p = malloc(size);
       if (p == NULL)
           err(1, NULL);
       fd = open(file_name, O_RDONLY, 0);
       if (fd == -1)
           err(1, "%s", file_name);

   Display an error message and exit:

       if (tm.tm_hour < START_TIME)
           errx(1, "too early, wait until %s", start_time_string);

   Warn of an error:

       fd = open(raw_device, O_RDONLY, 0);
       if (fd == -1)
           warnx("%s: %s: trying the block device",
                   raw_device, strerror(errno));
       fd = open(block_device, O_RDONLY, 0);
       if (fd == -1)
           err(1, "%s", block_device);


   error(3), exit(3), perror(3), printf(3), strerror(3)


   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.

Free Software

Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.

Free Books

The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.