Hardware: rpi 2
Internet access: ethernet at home
YunoHost version: Latest stretch download just installed today
(How do you get the version number>)
Error message : The server closed the connection instead of answering it, has nginx been restarted by error? (Error code/message: 0 error)
So what if you try to refresh the webadmin ? Do you see the app installed ?
No. Only Wordpress (my first install)
Well uh can you find any log for the failed install, if you go from the Home admin page, in Tools, Logs ?
Will get back to you in a few hours…
OK–I tried to install again and now I get the following:
The operation ‘Install ‘roundcube’ application’ has failed! To get help, please provide the full log of this operation by clicking here
The SSOwat configuration has been generated
userdel: nscd did not terminate normally (signal 11)
userdel: nscd did not terminate normally (signal 11)
userdel: nscd did not terminate normally (signal 11)
userdel: nscd did not terminate normally (signal 11)
Remove the user roundcube
E: Unable to locate package roundcube-ynh-deps
Removing database roundcube
The operation ‘Install ‘roundcube’ application’ has failed! To get help, please provide the full log of this operation by clicking here
!!
roundcube’s script has encountered an error. Its execution was cancelled.
!!
require [–dev] [–prefer-source] [–prefer-dist] [–no-progress] [–no-suggest] [–no-update] [–no-scripts] [–update-no-dev] [–update-with-dependencies] [–update-with-all-dependencies] [–ignore-platform-reqs] [–prefer-stable] [–prefer-lowest] [–sort-packages] [-o|–optimize-autoloader] [-a|–classmap-authoritative] [–apcu-autoloader] [–] []…
proc_open(): fork failed - Cannot allocate memory
[ErrorException]
PHP Warning: proc_open(): fork failed - Cannot allocate memory in phar:///var/www/roundcube/composer.phar/vendor/symfony/console/Application.php on line 952
Check https://getcomposer.org/doc/articles/troubleshooting.md#proc-open-fork-failed-errors for details
The following exception is caused by a lack of memory or swap, or not having swap configured
useradd: nscd did not terminate normally (signal 11)
useradd: nscd did not terminate normally (signal 11)
useradd: nscd did not terminate normally (signal 11)
useradd: nscd did not terminate normally (signal 11)
dpkg-preconfigure: unable to re-open stdin:
debconf: falling back to frontend: Teletype
debconf: (This frontend requires a controlling tty.)
debconf: unable to initialize frontend: Readline
debconf: falling back to frontend: Readline
debconf: (Dialog frontend will not work on a dumb terminal, an emacs shell buffer, or without a controlling terminal.)
debconf: unable to initialize frontend: Dialog
Well uh … that looks like you don’t have enough memory (RAM) available to do this …
Do you have a lot of stuff installed already on your server ? What does free -h tells ?
This was a new install as of yesterday and I just installed 1 other app. On a new 32G SD card. I think I’m going to reinstall from scratch since the OS just crashed with some kind of journaling error while just sitting there.
root@jim:~# free -h
total used free shared buff/cache available
Mem: 433M 113M 120M 12M 199M 257M
Swap: 99M 45M 54M
root@jim:~# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/root 30G 2.3G 26G 8% /
devtmpfs 213M 0 213M 0% /dev
tmpfs 217M 0 217M 0% /dev/shm
tmpfs 217M 5.9M 211M 3% /run
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 217M 0 217M 0% /sys/fs/cgroup
/dev/mmcblk0p1 44M 23M 22M 51% /boot
tmpfs 44M 0 44M 0% /run/user/0
root@jim:~#
Alright but if you reinstalled and don’t have the exact same setup with the same apps installed, there’s no point anymore trying to run this … Just maybe attempt to reinstall the app to see if the issue is still there 
I did and it’s still there. Fork failed–Cannot allocate memory.
Hello,
My Raspberry Pi still freeze sometimes and don’t respond very well because of the load.
So I’ve increased the swapfile from 100 to 1024 Mo.
sudo nano /etc/dphys-swapfile
CONF_SWAPFILE=100 → CONF_SWAPFILE=1024
sudo /etc/init.d/dphys-swapfile restart
Source : Increase size of existing swap file - Raspberry Pi Forums
ppr
Are you sure that you are on a RPi2 ? RPi2 are supposed to have 1 GB of RAM, not 512 MB 
It’s the only pi I’ve got. In a previous installation (on the same pi) I had several apps installed with no problem. (Though I used rainloop instead of roundcube)
Well done 
Increasing the swap to 1K fixed the problem!