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.
{
    if (value.isNull()) return std::nullopt;
    if (value.isBool()) return value.get_bool();
    return InterpretBool(value.get_str());
}
bool SettingToBool(const util::SettingsValue& value, bool fDefault)
{
    return SettingToBool(value).value_or(fDefault);
}
bool ArgsManager::SoftSetArg(const std::string& strArg, const std::string& strValue)
{
    LOCK(cs_args);
    if (IsArgSet(strArg)) return false;
    ForceSetArg(strArg, strValue);
    return true;
}
bool ArgsManager::SoftSetBoolArg(const std::string& strArg, bool fValue)
{
    if (fValue)
        return SoftSetArg(strArg, std::string("1"));
    else
        return SoftSetArg(strArg, std::string("0"));
}
void ArgsManager::ForceSetArg(const std::string& strArg, const std::string& strValue)
{
    LOCK(cs_args);
    m_settings.forced_settings[SettingName(strArg)] = strValue;
}
void ArgsManager::AddCommand(const std::string& cmd, const std::string& help)