c - Linux getpwnam() library dependencies -



c - Linux getpwnam() library dependencies -

i had programme scheme phone call getpwnam() failing @ runtime. debug this, decided run getpwnam() in isolation code (it came forum):

#include <pwd.h> #include <stdio.h> #include <stdlib.h> int main(int argc, char **argv) { struct passwd *pw; if (argc != 2) { printf("usage: %s username\n", argv[0]); exit(0); } pw = getpwnam(argv[1]); if (pw == null) printf("getpwnam failed\n"); else printf("home dir = %s\n", pw->pw_dir); exit(0); }

oddly seems depend on libnss_compat-2.3.5.so beingness present:

with libnss_compat:

./pwnam root home dir = /root

without libnss_compat:

./pwnam root getpwnam failed

so question is; why getpwnam() dependent on libnss_compat*.so? found out nm -d command libc-2.3.5.so lib provides getpwnam().

readelf -d shows me libc in turn depends on ld.so.1. in turn depends on nothing. why on earth libnss_compat having impact?

thanks help everyone!!

nss name service switch, library can user info in various sources (traditional password files, network info service, ldap). getpwnam may defined in libc, load actual nss library @ runtime. looking within libc, find

$ strings /lib/x86_64-linux-gnu/libc.so.6 | grep libnss libnss_ libnss_ libnss_%s.so.%d.%d

the lastly line format string snprintf used build name of actual implementation library load using dlopen. implementation determined using /etc/nsswitch.conf.

edit found place in glibc sources the library loaded. it's not (no longer?) using snprintf, principle still same.

c linux

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