| errors | Package errors implements functions to manipulate errors. |
| io/ioutil | Package ioutil implements some I/O utility functions. |
| math/rand | Package rand implements pseudo-random number generators suitable for tasks such as simulation, but it should not be used for security-sensitive work. |
| os | Package os provides a platform-independent interface to operating system functionality. |
| syscall | Package syscall contains an interface to the low-level operating system primitives. |
| time | Package time provides functionality for measuring and displaying time. |