int capng_change_id(int uid, int gid, capng_flags_t flag);
This function will change uid and gid to the ones given while retaining the capabilities previously specified in capng_update. It is not necessary and perhaps better if capng_apply has not been called prior to this function so that all necessary privileges are still intact. The caller is required to have CAP_SETPCAP capability still active before calling this function.
This function also takes a flag parameter that helps to tailor the exact actions performed by the function to secure the environment. The option may be or'ed together. The legal values are:
- Simply change uid and retain specified capabilities and that's all.
- After changing id, remove any supplement groups that may still be in effect from the old uid.
- After changing id, initialize any supplement groups that may come with the new account. If given with CAPNG_DROP_SUPP_GRP it will have no effect.
After changing the uid and gid, clear the bounding set regardless to the internal representation already setup.
This returns 0 on success and a negative number on failure. -1 means capng has not been initted properly, -2 means a failure requesting to keep capabilities across the uid change, -3 means that applying the intermediate capabilities failed, -4 means changing gid failed, -5 means dropping supplemental groups failed, -6 means changing the uid failed, -7 means dropping the ability to retain caps across a uid change failed, -8 means clearing the bounding set failed, -9 means dropping CAP_SETPCAP failed, -10 means initializing supplemental groups failed.
Note: the only safe action to do upon failure of this function is to probably exit. This is because you are likely in a situation with partial permissions and not what you intended.