Startup disk has space on restart but suddenly fills up

[bok]

I'm having a problem where when I start up my macbook (2014 macbook air, El Capitan), it has about 33GB of space on the HD, but after a few hours of use I get a startup disk full error. Then I restart and it goes back to having 33GB free space.

I went on a library clear out spree a while ago, so I'm wondering if that has something to do with it? I don't use the mail app, but I used to, and it had heaps of attachment files that I deleted - maybe I messed something up doing that?

Have run first aid on the drive, and had a bit of a search of old threads, but haven't yet found a solution. Any help much appreciated!! Thank you.

 

[ferrarr]

Do you use Time Machine? It creates local snapshots, which could be doing that?

https://support.apple.com/en-us/HT204015
https://www.macworld.com/article/3260635/macs/how-to-delete-time-machine-snapshots-on-your-mac.html

 

[Slydude]

What is the total capacity of the hard drive? Also what types of tasks are you typically performing as the free space diminishes?

In order to run efficiently the OS creates swap files -- especially if it doesn't have enough free ram. On top of those swap files some programs create additional swap files thus using even more hard drive space and memory. Over time, these fiels can get quite large.

 

[MacInWin]

How big is the drive? 33GB sounds large, but you should leave about 10% of an SSD free, 15% of an HD. So if it's a 1TB drive, 33GB isn't enough free space.

 

[IWT]

To add to Jake's excellent advice and to give some background to it, here are two articles.

The first from July 2018 is fairly dogmatic on the matter - 15% minimum free space on both HDD and SSD.

The second from 2017 is more flexible in its approach. The initial answers tend towards the 15% minimum; but on being challenged to back this up, there follows a broader discussion with published references.

You will gather that this is a controversial subject; but for bok (the OP) to have only 32GB free space, is really pushing things to the limit.

https://www.lifewire.com/how-much-free-drive-space-needed-2260187
https://superuser.com/questions/1256074/how-much-space-to-leave-free-on-hdd-or-ssd

Ian