fai-setup: E: You don't have enough free space in /var/cache/apt/archives/.

[Thomas Lange]

    >    procube at fai-server:~$ df -i
    >    Filesystem      Inodes  IUsed   IFree IUse% Mounted on
    >    /dev/dm-0      2469152 114985 2354167    5% /
    >    udev             27460    333   27127    2% /dev
    >    tmpfs            29481    475   29006    2% /run
    >    tmpfs            29481      1   29480    1% /dev/shm
    >    tmpfs            29481      5   29476    1% /run/lock
    >    tmpfs            29481     13   29468    1% /sys/fs/cgroup
    >    /dev/sda1        62248    328   61920    1% /boot
    >    tmpfs            29481      6   29475    1% /run/user/116
    >    tmpfs            29481      4   29477    1% /run/user/1000

The problem is that fai-make-nfsroot is using a ramdisk (tmpfs) for
speed up in var/lib/dpkg and /var/cache inside the nfsroot. Your host
(I guess a VM) has only very few RAM, so tmpfs is only of size
24M. You have to change the tmpfs size so all packages fit into /var
during download.

-- 
regards Thomas