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.
{
    LOCK(cs_dir_locks);
    fs::path pathLockFile = directory / lockfile_name;
    
    if (dir_locks.count(fs::PathToString(pathLockFile))) {
        return true;
    }
    
    FILE* file = fsbridge::fopen(pathLockFile, "a");
    if (file) fclose(file);
    auto lock = std::make_unique<fsbridge::FileLock>(pathLockFile);
    if (!lock->TryLock()) {
        return error("Error while attempting to lock directory %s: %s", fs::PathToString(directory), lock->GetReason());
    }
    if (!probe_only) {
        
        dir_locks.emplace(fs::PathToString(pathLockFile), std::move(lock));
    }
    return true;
}
void UnlockDirectory(const fs::path& directory, const fs::path& lockfile_name)