On my Linux Mint 19.1:
```bash
$ umask
0022
```

After the first run of `bitcoin-qt -sysperm=false` the `0700` permissions are expected for both the datadir (`~/.bitcoin`) and the walletdir (`~/.bitcoin/wallets`).

Actually, the directories are created with such access permissions:
```bash
$ stat ~/.bitcoin | grep Uid
Access: (0755/drwxr-xr-x)  Uid: ( 1000/ hebasto)   Gid: ( 1000/ hebasto)
$ stat ~/.bitcoin/wallets | grep Uid
Access: (0755/drwxr-xr-x)  Uid: ( 1000/ hebasto)   Gid: ( 1000/ hebasto)
```

Refs:
- #4286
- #13371
- #13389

NOTE: reading through the initial PR #4286 makes me think it was controversial. Is it a better and simpler way to just get rid of `-sysperm` option? I believe a user who needs this option can easily run `chown` command.
registerSignalHandler(SIGHUP, HandleSIGHUP);
    
    signal(SIGPIPE, SIG_IGN);
#else
    SetConsoleCtrlHandler(consoleCtrlHandler, true);
#endif
    std::set_new_handler(new_handler_terminate);
    return true;
}
bool AppInitParameterInteraction(const ArgsManager& args, bool use_syscall_sandbox)
{
    const CChainParams& chainparams = Params();
    
    
    
    
    
    std::string network = args.GetChainName();
    if (network == CBaseChainParams::SIGNET) {
        LogPrintf("Signet derived magic (message start): %s\n", HexStr(chainparams.MessageStart()));
    }
    bilingual_str errors;
    for (const auto& arg : args.GetUnsuitableSectionOnlyArgs()) {
        errors += strprintf(_("Config setting for %s only applied on %s network when in [%s] section.") + Untranslated("\n"), arg, network, network);
    }
    if (!errors.empty()) {
        return InitError(errors);
    }
    
    bilingual_str warnings;