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 (strValue.empty())
        return true;
    return (LocaleIndependentAtoi<int>(strValue) != 0);
}
static std::string SettingName(const std::string& arg)
{
    return arg.size() > 0 && arg[0] == '-' ? arg.substr(1) : arg;
}
struct KeyInfo {
    std::string name;
    std::string section;
    bool negated{false};
};
/**
 * Parse "name", "section.name", "noname", "section.noname" settings keys.
 *
 * @note Where an option was negated can be later checked using the
 * IsArgNegated() method. One use case for this is to have a way to disable
 * options that are not normally boolean (e.g. using -nodebuglogfile to request
 * that debug log output is not sent to any file at all).
 */
KeyInfo InterpretKey(std::string key)