What causes "%s " in rustdesk/rustdesk?

Note the library named at the start of the printed line — that is the missing dependency

%s

Error message

%s

What it means

Immediately after the 'Failed to load "librustdesk.so"' message, the wrapper prints the raw dlerror() string. This is the actual reason the system-wide dlopen failed — classically '<lib>.so: cannot open shared object file: No such file or directory' — and the code then parses that pattern to offer a package-install hint.

Source

Thrown at flutter/linux/main.cc:48

  if (!librustdesk) {
    char* error = dlerror();
    if (error != nullptr) {
      fprintf(stderr, "Failed to load \"%s\": %s\n", lib_path, error);
    }
  }
  return librustdesk;
}

bool flutter_rustdesk_core_main() {
   void* librustdesk = dlopen_bundled_lib();
   if (!librustdesk) {
      librustdesk = dlopen(RUSTDESK_LIB_PATH, RTLD_LAZY);
   }
   if (!librustdesk) {
      fprintf(stderr,"Failed to load \"librustdesk.so\"\n");
      char* error;
      if ((error = dlerror()) != nullptr) {
        fprintf(stderr, "%s\n", error);
        char* libmissed = strstr(error, ": cannot open shared object file: No such file or directory");
        if (libmissed != nullptr) {
          *libmissed = '\0';
          char* so = strdup(error);
          print_help_install_pkg(so);
          free(so);
        }
      }
     return false;
   }
   auto core_main = (RustDeskCoreMain) dlsym(librustdesk,"rustdesk_core_main");
   char* error;
   if ((error = dlerror()) != nullptr) {
       fprintf(stderr, "Program entry \"rustdesk_core_main\" is not found: %s\n", error);
       return false;
   }
   return core_main();
}

View on GitHub (pinned to 7aa98d43cf)

Solutions

Note the library named at the start of the printed line — that is the missing dependency
Install it via the distro package manager (the program prints a suggested command for common cases)
Find the providing package with dnf provides / apt-file search / archweb pkgfile
Re-run rustdesk after installing; no rebuild is needed

Defensive patterns

Strategy: fallback

Validate before calling

# Parse launch logs for the dlerror line and resolve the named library (shell)
ldd /opt/rustdesk/lib/librustdesk.so | awk '/not found/{print $1}'

Prevention

Always read the line following 'Failed to load' — it names the missing dependency
Resolve dependencies with the distro's provides-search (dnf provides, apt-file search) instead of manual .so downloads
Keep a container/VM per supported distro to validate loadability before release

When it happens

Trigger: dlopen failed and dlerror() returns non-NULL; the wrapper strstr-matches ': cannot open shared object file: No such file or directory' to extract the missing library name and call print_help_install_pkg.

Common situations: Missing transitive dependency such as libnsl.so.1, libclang.so, or an outdated libcrypto on the host; versioned .so mismatch after a system upgrade.

Related errors

AI-assisted analysis of rustdesk/rustdesk@7aa98d43cf (2026-08-16). Data as JSON: /api/errors/b22caee097e0eb49. Report an issue: GitHub.