This is daemons/become_daemon.h (Listing 37-1, page 770), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

  Cover of The Linux Programming Interface
+/* become_daemon.h
+   Header file for become_daemon.c.
 #ifndef BECOME_DAEMON_H             /* Prevent double inclusion */
 /* Bit-mask values for 'flags' argument of becomeDaemon() */
 #define BD_NO_CHDIR           01    /* Don't chdir("/") */
 #define BD_NO_CLOSE_FILES     02    /* Don't close all open files */
 #define BD_NO_REOPEN_STD_FDS  04    /* Don't reopen stdin, stdout, and
                                        stderr to /dev/null */
 #define BD_NO_UMASK0         010    /* Don't do a umask(0) */
 #define BD_MAX_CLOSE  8192          /* Maximum file descriptors to close if
                                        sysconf(_SC_OPEN_MAX) is indeterminate */
 int becomeDaemon(int flags);

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