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seteuid, setegid - set effective user or group ID
#include <sys/types.h> #include <unistd.h> int seteuid(uid_t euid); int setegid(gid_t egid); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): seteuid(), setegid(): _BSD_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600
seteuid() sets the effective user ID of the calling process. Unprivileged user processes may only set the effective user ID to the real user ID, the effective user ID or the saved set-user-ID. Precisely the same holds for setegid() with "group" instead of "user".
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
EPERM The calling process is not privileged (Linux: does not have the CAP_SETUID capability in the case of seteuid(), or the CAP_SETGID capability in the case of setegid()) and euid (respectively, egid) is not the real user (group) ID, the effective user (group) ID, or the saved set-user-ID (saved set-group-ID).
Setting the effective user (group) ID to the saved set-user-ID (saved set-group-ID) is possible since Linux 1.1.37 (1.1.38). On an arbitrary system one should check _POSIX_SAVED_IDS. Under libc4, libc5 and glibc 2.0 seteuid(euid) is equivalent to setreuid(-1, euid) and hence may change the saved set-user-ID. Under glibc 2.1 and later it is equivalent to setresuid(-1, euid, -1) and hence does not change the saved set-user-ID. Similar remarks hold for setegid(). According to POSIX.1, seteuid() (setegid()) need not permit euid (egid) to be the same value as the current effective user (group) ID, and some implementations do not permit this.
geteuid(2), setresuid(2), setreuid(2), setuid(2), capabilities(7), credentials(7)
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