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.
{
    KeyInfo result;
    
    size_t option_index = key.find('.');
    if (option_index != std::string::npos) {
        result.section = key.substr(0, option_index);
        key.erase(0, option_index + 1);
    }
    if (key.substr(0, 2) == "no") {
        key.erase(0, 2);
        result.negated = true;
    }
    result.name = key;
    return result;
}
/**
 * Interpret settings value based on registered flags.
 *
 * @param[in]   key      key information to know if key was negated
 * @param[in]   value    string value of setting to be parsed
 * @param[in]   flags    ArgsManager registered argument flags
 * @param[out]  error    Error description if settings value is not valid
 *
 * @return parsed settings value if it is valid, otherwise nullopt accompanied
 * by a descriptive error string
 */
static std::optional<util::SettingsValue> InterpretValue(const KeyInfo& key, const std::string* value,