rpm complains about insufficient disk space

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Environment

SUSE Linux Enterprise Server
SUSE Linux Enterprise Desktop

Situation

Assuming kernel-source package needs to be installed.

Trying to install kernel-source through yast fails with:

Subprocess failed. Error: RPM failed: installing package kernel-source-4.12.14-95.32.1.noarch needs 377MB on the /usr/src filesystem

After that the rpm is stored in e.g.
/var/cache/zypp/packages/SMT-http_lab-solar_system_com:SLES12-SP4-Updates/noarch

Trying to install from there with rpm -Uv

rpm -Uv kernel-source-4.12.14-95.32.1.noarch.rpm
Preparing packages...
installing package kernel-source-4.12.14-95.32.1.noarch needs 377MB on the /usr/src filesystem

Which is confusing since there is more space available like:

honey123:~ # df -h /usr/src
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/system-src 3.9G 3.2G 426M 89% /usr/src

Resolution

Free more space than it seems to need on the first look.

The error message is both correct and misleading.

After freeing up some disk space:

honey123:~ # df -h /usr/src
Filesystem              Size Used Avail Use% Mounted on
/dev/mapper/system-src   3.9G 2.7G 959M 75% /usr/src

rpm -Uv kernel-source-4.12.14-95.32.1.noarch.rpm
Preparing packages...
kernel-source-4.12.14-95.32.1.noarch

After installation:

honey123:~ # df -h /usr/src
Filesystem              Size Used Avail Use% Mounted on
/dev/mapper/system-src 3.9G 3.5G 196M 95% /usr/src

Difference 959-196=763Mb

What the message actually means is: 377Mb more....426Mb+377Mb=803Mb
763Mb plus a little overhead as the package needs to be extracted and uncompressed during installation.

Cause

Strictly speaking, rpm is right and it's just a question of how to read and understand the message.

It could be more userfriendly but since there were a couple discussions over years and nothing changed it's not expected that it will in the near future.

Disclaimer

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