Root partition is suddenly 100% full - can't log in

Okay, I may have solved this. I installed the simple backup tool earlier this week and set it up to write backups to a second HD. The partition was /dev/sdb2 and was supposed to be mounted at /media/sdb2. However, when I ran the backup, I don't think /dev/sdb2 was mounted. So rather than writing the backup to the separate device, I think it wrote the backup to a directory /media/sdb2.

Is that a plausible solution? I booted the recovery mode and then deleted everything in /media/sdb2. After that the / partition was back to 75% empty so I guess that's what happened.

I'm leaving this open for a bit to see if anyone can confirm this and to suggest a better way to run backups.

Thanks.

Couple of observations Jim:

1) it seems strange that a backup of 25% of the disk filled it up completely; perhaps it was a recursive backup?

2) there should have been a reserve set on that HD, so that you could have logged as root and investigated. Did you try that?

1) the back up was of my /home partition which is about 60GB in size and should have been written to a second hard drive that seems to have not been mounted at the time of the backup so it defaulted to an actual directory on /media rather than a mounted device. It seems to have written about 16GB to my / partition and filled it up. I was only able to observe this from a recovery console and only after a bit of investigating since the directory "looked" like my mounted backup partition but in fact was actually written to a directory on /. Confusing.

2) I was not at all able to log in. I got the "your session lasted less than 10 seconds" message. Booting the recovery mode I was able to use df and see that indeed the / partition was 100% full. There doesn't seem to have been any "reserve" space. Should that be set up by default or is it something I do manually if I want it? If it should have been automatic - it wasn't, so that suggests a bug.

Thanks for the feedback. I seem to love screwing up my system (but I also love that I'm getting better and figuring it out). This one really had me confused for a while and troubleshooting from CLI was an experience.

The reserve is something you setup, usually during partitioning. If you used gparted, or you partitioned during install, you should have set an amount (default 5% IIRC) aside which is indeed what made it possible for you to login in recovery mode.
You can see that for instance if you do a df, and you will see that available is not total minus used.
You can change the allocation also using a tool, like tune2fs.

Hello Cesare, Jim,

Far from me in getting into Jim's problem -it looks that it's already sorted out. Just a comment

I know well from my own past experience the frustrations related to backups/restore operations -they are pretty tricky to say the least, every backup/restore app be it under win or linux has a 'mind' of its own which MUST be 'mastered' well before proceeding (and this goes well back to the time of DOS diskettes, tape drives etc). So, after a couple of 'incidents' I decided to get to the bottom of this and find a reliable and, v important, logical easy to understand and use app that fullfils that important task.

For more than 5 years I'm using to backup/restore partitions/files to/from image files either to CD/DVD or other HD's in the latter case prefferably external HD's. I must say that since I took that decision that 'chapter' called backup/restore is for all tense and purposes closed for me -no more surprises and 'incidents'. Basically, I'm using a utility written under the good old dos by terabyte

http://www.terabyteunlimited.com

that installs beautifully from guess what -a good old 1.44 floppy creating an extended MBR and installing itself in less than 8MB that does marvellous things. I'm not going into the nitty-gritty of it; it is available for trial purposes and if the user likes it it can be had for a nominal amount. Under the same url one can find also Image for DOS and Image for Linux apps. I'm using BootitNG that basically is a 'all-in-one' type of app. Give it a try Gents and tell me here what's your opinion.

Best regards,
peter b