cannot resolve "No space left on device"

Question

I'm installing one package while getting the error that Could not install packages due to an EnvironmentError: [Errno 28] No space left on device However, I'm pretty sure my space is sufficiently empty and mostly unused.

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UPDATE: The result I get after running df -h --exclude-type=squashfs

Filesystem      Size  Used Avail Use% Mounted on
udev            7.6G     0  7.6G   0% /dev
tmpfs           1.6G  2.2M  1.6G   1% /run
/dev/sda6       294G   27G  253G  10% /
tmpfs           7.6G  135M  7.5G   2% /dev/shm
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           7.6G     0  7.6G   0% /sys/fs/cgroup
/dev/sda7        32G   31G  5.6M 100% /home
tmpfs           1.6G   16K  1.6G   1% /run/user/120
tmpfs           1.6G  144K  1.6G   1% /run/user/1000

The result I get after running df -i --exclude-type=squashfs:

Filesystem       Inodes  IUsed    IFree IUse% Mounted on
udev            1971614    627  1970987    1% /dev
tmpfs           1980471   1287  1979184    1% /run
/dev/sda6      19570688 407691 19162997    3% /
tmpfs           1980471    166  1980305    1% /dev/shm
tmpfs           1980471      7  1980464    1% /run/lock
tmpfs           1980471     18  1980453    1% /sys/fs/cgroup
/dev/sda7       2125760 634515  1491245   30% /home
tmpfs           1980471     24  1980447    1% /run/user/120
tmpfs           1980471     70  1980401    1% /run/user/1000

As you can see the root folder and home folder is only used left than 10%. So far I checked some sources and some answers suggest that it is because of /tmp. I tried to unmount but the problem persists. Can someone offer me some suggestions and possible solutions for it? Thanks a lot.

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NEW UPDATE

output of du -sh /home:

du: cannot read directory '/home/lost+found': Permission denied
du: cannot read directory '/home/danni/.splunk': Permission denied
du: cannot read directory '/home/danni/.cache/doc': Permission denied
du: cannot read directory '/home/danni/.cache/netease-cloud-music/Cef/Cache/Local Storage': Permission denied
du: cannot read directory '/home/danni/.cache/netease-cloud-music/Cef/Cache/Cache': Permission denied
du: cannot read directory '/home/danni/.cache/dconf': Permission denied
30G /home