When I chose to install Ubuntu alongside my Mac OS I saw no option to choose how big I wanted my install to be. It installed it and booted from the installed Ubuntu, and It looks fine, but how can I resize the partition so I have free space again?
if you installed ubuntu "alongside" mac then you should ABSOLUTELY NOT use a partition wizard nor resize the partition of ubuntu because it will be on the same partition.
if you find that ubuntu is, in fact, installed on a SEPARATE partition, then follow my advice below.
if in doubt, just uninstall ubuntu (that would be a separate topic) and make sure, before you install it again, that you have made a separate partition for ubuntu to read as you may not have already had a partition specifically for ubuntu already made.
ive run in to this before where i have not been able to create a partition for ubuntu within the installer but when i created one beforehand i was able to figure out where to go from there within the installer.
it is also good to create a back-up partition as well and make sure that you LABEL THEM with a familiar name when you create them so you do not lose track of which one is which.
the way to find out if ubuntu is on a separate partition is to open a partition wizard of your choice and find out which partition is ubuntu, and which one is mac.
if there is only one partition then do not proceed to my below advice as it will just resize the partition with ubuntu and mac on it and could lead to errors if you are going to uninstall ubuntu and reinstall . .
if you find (FOR SURE) that ubuntu is in fact installed on a separate partition then follow my advice below.
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just install a partition manager from the ubuntu software center or a partition manager in mac (from wherever you get your software from) .
make sure it has a good reputation and once you find one after a little bit of research, it will do the work for you after you figure out how to use it.
it might take a while once you start the process as it has to move all the files and make sure that there arent any stray ones that might get deleted AND move the ones it does find as well, so be patient once you have started the process.
remember, each partition manager has its own way to use it, but, they all basically do the same thing.
i am pretty new to ubuntu and ive done this before easily, the answer is yes, it can be done after you install, it just might take a minute.
my advice is to use wich operating system you are most comfortable with to do the partition resizing. ubuntu and mac both have good partition wizards as far as i am aware it is just a matter of preference to you of which one you are more comfortable working with right now.
i hesitate to suggest one specific answer because i dont know how experienced you are at this, but, id say after not more than a month of using ubuntu id found a partition program that did it all from ubuntu.
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like i said, you are going to want to have ubuntu on a separate partition before you resize it or it will just resize ubuntu and mac together as they are installed pretty much on the same partition, otherwise . . .