Help reinstalling macOS

User wrote " So my Macbook won't boot up and the internet recovery gives me a -2001f error message. " The error message -2001f indicates there is a very weak or No Internet Connection

To achieve the Internal Recovery Mode - command + Option + r key and Immediately look for the Wifi Icon.

You will have to click click on the Icon and Manually Input the wifi Password. To avoid this tricky method better to connect via Ethernet Cable to Router.

Further, even if you can download the Full Installer ( doubtful ) on a Windows PC - the Create a Bootable Installer can not be done on any other platform but from an Apple Computer

The first mistake was to erase your macs hard drive without having a means to reinstall the OS,

you should not rely on Apples Recovery Servers.

You should have downloaded a copy of macOS High Sierra and created a bootable USB flash drive installer,

and used that to erase your drive and install macOS High Sierra.

Transmac does not work for creating bootable flash drives for macOS.

Are you able to borrow another mac, and download macOS High Sierra and then create a bootable

USB installer on that mac. Then use that to install macOS High Sierra.

Mac OS X Base System is Apples Servers.

If you can't borrow a mac, then you may have to try the Apple Recovery Servers.

Boot to your Recovery HD, restart the mac while pressing and holding down the Command and R keys.

Open Disk Utility, click on View in the menubar and select Show All Devices.(Select All Devices will be on macs running

High Sierra or newer)

Highlight the Disk not any of the indented Volumes (Disk is called Apple SSD SM0....)

Click Erase.

Give the Disk a name.

Format: APFS (for macOS High Sierra) or Mac OS X Extended (Journaled) {for macOS Sierra or earlier}

Scheme: GUID Partition Map.

Click Erase.

When Done quit Disk Utility.

The certificates for several of Apples OS's expired in October 2019, Apple haven’t bothered getting these updated on 

their Recovery Servers with valid certificates. 

This may be the problem you are experiencing. 

Try this workaround, we are going to set the time and date on your mac to a date previous to the expiry date of the certificates.

Connect your mac to your router via cable, not WiFi

Boot to your Recovery HD, click on Utilities in the menubar select Terminal.

Make sure WiFi is switched off, it can reset the date back to today.

Enter a new date, for example or just copy and paste

sudo date -u 011421002017

press Return

enter your password

press Return

If Terminal returns an error saying sudo : command not found, then try again without sudo.

just enter 

date -u 011421002017

press Return

You won't be prompted for a Password if you did not need to use sudo

Once the date has changed you can quit Terminal.

Now try downloading the OS.

Click on Install OS X, press Continue.

If this works then when the OS is installed and booted up you can Open System Preferences> Date & Time

and reset the time back to today.

One can in 2 cm for Router on Wifi and still not have a connection. If the Wifi is active AND the Ethernet connect is also active - turn OFF Wifi and use Ethernet connection ONLY. Once can not use Both at the same time.