Question: I'm working with Swift in Ubuntu, and I am getting an error that arc4random is an unresolved identifier. More information on this known bug [here](https://bugs.swift.org/browse/SR-685). Basically, the function only exists in BSD distros. I've tried module mapping header files, apt-getting packages, and I get more and more errors, which is not worth pursuing since this one function is not used very often.

Are there any functions to get pseudo random numbers with an upper-bound parameter that is compatible with Swift in Linux?

Answer: 
If generating a random number *within a function*, using `srandom(UInt32(time(nil)))` **inside the function** can produce the same random number every time.

Instead, prepare the random seed at the top of your `main.swift` once, and then random should behave as expected throughout.

Example:
--------

```
//
//  main.swift
//  Top of your code
//

import Foundation

#if os(Linux)
    srandom(UInt32(time(nil)))
#endif

func getRandomNum(_ min: Int, _ max: Int) -> Int {
    #if os(Linux)
        return Int(random() % max) + min
    #else
        return Int(arc4random_uniform(UInt32(max)) + UInt32(min))
    #endif
}

// Print random numbers between 1 and 10
print(getRandomNum(1, 10))
print(getRandomNum(1, 10))
print(getRandomNum(1, 10))
print(getRandomNum(1, 10))
print(getRandomNum(1, 10))

```

Swift on Linux (Ubuntu in my case) will produce the same number every time if you put the `srandom` call inside my `getRandomNum` function.

Note of Caution:
----------------

`srandom` and `random` do not create a "truly" random number, and can be a security concern when making mission-critical applications that would be a target of a hack. The only real solution in that case is to execute Linux's `/dev/random` directly via `Process()`, and using its result. But this is outside the scope of the question.
You could try something like this? 

```
    #if os(Linux)
       random()
    #else
        arc4random_uniform()
    #endif

```