setresuid, setresgid - set real, effective and saved user or group ID
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <unistd.h> int setresuid(uid_t ruid, uid_t euid, uid_t suid); int setresgid(gid_t rgid, gid_t egid, gid_t sgid);
setresuid() sets the real user ID, the effective user ID, and the saved set-user-ID of the calling process. An unprivileged process may change its real UID, effective UID, and saved set-user-ID, each to one of: the current real UID, the current effective UID or the current saved set-user-ID. A privileged process (on Linux, one having the CAP_SETUID capability) may set its real UID, effective UID, and saved set-user-ID to arbitrary values. If one of the arguments equals -1, the corresponding value is not changed. Regardless of what changes are made to the real UID, effective UID, and saved set-user-ID, the filesystem UID is always set to the same value as the (possibly new) effective UID. Completely analogously, setresgid() sets the real GID, effective GID, and saved set-group-ID of the calling process (and always modifies the filesystem GID to be the same as the effective GID), with the same restrictions for unprivileged processes.
On success, zero is returned. On error, -1 is returned, and errno is set appropriately. Note: there are cases where setresuid() can fail even when the caller is UID 0; it is a grave security error to omit checking for a failure return from setresuid().
EAGAIN The call would change the caller's real UID (i.e., ruid does not match the caller's real UID), but there was a temporary failure allocating the necessary kernel data structures. EAGAIN ruid does not match the caller's real UID and this call would bring the number of processes belonging to the real user ID ruid over the caller's RLIMIT_NPROC resource limit. Since Linux 3.1, this error case no longer occurs (but robust applications should check for this error); see the description of EAGAIN in execve(2). EINVAL One or more of the target user or group IDs is not valid in this user namespace. EPERM The calling process is not privileged (did not have the necessary capability in its user namespace) and tried to change the IDs to values that are not permitted. For setresuid(), the necessary capability is CAP_SETUID; for setresgid(), it is CAP_SETGID.
These calls are available under Linux since Linux 2.1.44.
These calls are nonstandard; they also appear on HP-UX and some of the BSDs.
Under HP-UX and FreeBSD, the prototype is found in <unistd.h>. Under Linux, the prototype is provided by glibc since version 2.3.2. The original Linux setresuid() and setresgid() system calls supported only 16-bit user and group IDs. Subsequently, Linux 2.4 added setresuid32() and setresgid32(), supporting 32-bit IDs. The glibc setresuid() and setresgid() wrapper functions transparently deal with the variations across kernel versions. C library/kernel differences At the kernel level, user IDs and group IDs are a per-thread attribute. However, POSIX requires that all threads in a process share the same credentials. The NPTL threading implementation handles the POSIX requirements by providing wrapper functions for the various system calls that change process UIDs and GIDs. These wrapper functions (including those for setresuid() and setresgid()) employ a signal-based technique to ensure that when one thread changes credentials, all of the other threads in the process also change their credentials. For details, see nptl(7).
getresuid(2), getuid(2), setfsgid(2), setfsuid(2), setreuid(2), setuid(2), capabilities(7), credentials(7), user_namespaces(7)
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 https://www.kernel.org/doc/man-pages/.
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 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.
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.