View Full Version : df command output

8th December 2009, 07:23 PM
Hey forum,

I recently purchased 4 external USB drives for backup use on various Fedora servers. I noticed after fdisk'ng and formatting all of them, attached to different sytems, df command output shows the following discrepencies:

[root@server ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sdb1 917G 200M 871G 1% /mnt/usb1
/dev/sdc1 917G 200M 871G 1% /mnt/usb2

Would someone explain to me why/how 917GB is listed as size, but only 871GB is listed as available?


8th December 2009, 08:14 PM
5% reserved for journaling/emergency:
.95 * 917 = 871


8th December 2009, 08:26 PM
I did not know that...thank you!

8th December 2009, 08:34 PM
You can disable or reduce this reserved space to get the 5% ( = ~46 GB in your case) back, if you really, really truly want/need to. I forget how though... . It's easy, I just can't remember off-hand the command. Search Forum if desired... .


8th December 2009, 08:55 PM
It's a backup drive, I did 'tune2fs -m 0 /dev/sdb1' to disable the space usage.

8th December 2009, 10:15 PM
Yeah, that was it: 'tune2fs -m 0 <device> '. IMHO, it makes sense to disable that reserved space in your case: external USB HDDs used for back-up purposes.


9th December 2009, 05:44 AM
It used to be, when you became superuser, you could use the reserved part for file storage. We would run out of non-superuser storage running large mine planning programs and they would die writing output. We would restart the job as superuser and it would finish.

I don't know if Linux will do that now or not.

10th December 2009, 02:37 PM
Actually I believe the reason behind it is if the / filesystem becomes full, root can still login and recover the system. Default setting of 5% is probably a bit high for todays disks.