I have a Django app with a postgresql backend. Postgresql creates temporary files every now and then - this can be a killer if disk space is critical (as is my case).
One way to alleviate the problem is to create a symlink to some other storage location where disk space isn't a bottleneck. In my case, postgresql stores temporary files at /$PGDATA/base/pgsql_tmp. I have a big SSD mounted at /mnt, so I want the temp files to reside there instead. The following ought to take care of this:
ln -sTf /mnt/pgsql_tmp $PGDATA/base/pgsql_tmp
chown -R postgres /mnt/pgsql_tmp #ensuring user 'postgres' has the right perms
chmod o+x /mnt
Before I do this in production, I decided to test this out locally. I created /mnt and /pgsql_tmp on my desktop, and then tried ln -sTf /home/hassan/Desktop/mnt/pgsql_tmp /home/hassan/Desktop/pgsql_tmp.
But this ends up giving me ln: ‘/home/hassan/Desktop/pgsql_tmp’: cannot overwrite directory. Can anyone point out what I'm doing wrong? Being a neophyte, I'm really trying to wrap my head around how this works.
Your best bet is to delete ~/pgsql_tmp, and let the ln command create it.
First note that LN doesn't link two objects; it creates a link to a target with a specific name from a place.
ln [OPTION]... [-T] TARGET LINK_NAME
When you create a link with ln, the NAME argument should indicate an object that does not yet exist, and it will be created as the result of the command. In your case you already created it (~/pgsql_tmp) as a directory.
Usually, You can use the -f switch to force deletion of anything already overlaping the NAME's path, but in your case you specified -T which means that you want to create the link as a File, not as a Directory. So when -f goes to overwrite the object at NAME, its trying to overwrite a directory with a file.
So, you can either create the link as a directory and use -f, or you can delete the object that overlaps NAME, and then create your link. The later is the best option.
#create a test target with a file, but without an object at lnname
~/tmp$ mkdir lntarget
~/tmp$ touch lntarget/contentfile1
~/tmp$ ln -sTf lntarget lnname
~/tmp$ ls ./lnname
contentfile1
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