This is namespaces/userns_functions.h, an example to accompany the book, The Linux Programming Interface.
This file is not printed in the book; it demonstrates Linux features that are not described in the book (typically features that have appeared since the book was published).
The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU Lesser General Public License, version 3.
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.
/* userns_functions.h Some useful auxiliary functions when working with user namespaces. */ #ifndef USERNS_FUNCTIONS_H /* Prevent double inclusion */ #define USERNS_FUNCTIONS_H #include <unistd.h> void display_creds_and_caps(char *str); int update_map(char *mapping, char *map_file); int proc_setgroups_write(pid_t child_pid, char *str); #endif
Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.