Have 'salloc' use $SHELL or /bin/sh as the fallback shell.

This is useful in situations where glibc’s Name Service Switch (NSS) is
dysfunctional (with ‘getpwuid’ returning NULL), which can happen when
/etc/nsswitch.conf specifies plugins that fail to be loaded in user code, for
instance because user code is linked against an incompatible libc.

Similar patch submitted upstream: https://bugs.schedmd.com/show_bug.cgi?id=19896

diff --git a/src/salloc/opt.c b/src/salloc/opt.c
index ffff7c8..74563ad 100644
--- a/src/salloc/opt.c
+++ b/src/salloc/opt.c
@@ -329,6 +329,7 @@ static void _opt_args(int argc, char **argv, int het_job_offset)
  * NOTE: This function is NOT reentrant (see getpwuid_r if needed) */
 static char *_get_shell(void)
 {
+	char *shell;
 	struct passwd *pw_ent_ptr;
 
 	if (opt.uid == SLURM_AUTH_NOBODY)
@@ -336,11 +337,13 @@ static char *_get_shell(void)
 	else
 		pw_ent_ptr = getpwuid(opt.uid);
 
-	if (!pw_ent_ptr) {
-		pw_ent_ptr = getpwnam("nobody");
-		warning("no user information for user %u", opt.uid);
+	if (pw_ent_ptr) {
+		shell = pw_ent_ptr->pw_shell;
+	} else {
+		shell = getenv("SHELL") ?: "/bin/sh";
+		warning("no user information for user %u, using '%s' as the shell", opt.uid, shell);
 	}
-	return pw_ent_ptr->pw_shell;
+	return shell;
 }
 
 static void _salloc_default_command(int *argcp, char **argvp[])
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<tr><td><span title='2023-04-21 16:16:38 +0200'>2023-04-21</span></td><td><a href='/guix/commit/tests/guix-download.sh?id=37dd69b44511dc73eb04bdebe8d82c9a0386338e'>tests: Fix checks for expected failures.</a><span class='msg-avail'>...<span class='msg-tooltip'>Addresses &lt;https://issues.guix.gnu.org/62406&gt;.

With 'set -e', a return status inverted with '!' does not cause the shell to
exit immediately.  Instead use '&amp;&amp; false' to indicate an expected failure.

* tests/guix-archive.sh, tests/guix-build-branch.sh, tests/guix-build.sh,
tests/guix-daemon.sh, tests/guix-download.sh,
tests/guix-environment-container.sh, tests/guix-environment.sh,
tests/guix-gc.sh, tests/guix-git-authenticate.sh, tests/guix-graph.sh,
tests/guix-hash.sh, tests/guix-home.sh, tests/guix-pack-relocatable.sh,
tests/guix-pack.sh, tests/guix-package-aliases.sh, tests/guix-package-net.sh,
tests/guix-package.sh, tests/guix-refresh.sh, tests/guix-shell.sh,
tests/guix-style.sh, tests/guix-system.sh: Replace uses of '! ...' with
'... &amp;&amp; false' or `test ! ...` as appropriate.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Eric Bavier</td></tr>