error message not very helpfull

[HenryNe]

On some errors where freelan breaks out, the error message was not helpfully, because only the error was printed, without a reference to the action.

For example on a vServer without rights to create the node /dev/net/tap, freelan terminates with follow messages:

root@srv:~# freelan -f -d -c /etc/freelan/freelan.conf
2020-03-22T12:34:29.569234 [INFORMATION] Reading configuration file at: "/etc/freelan/freelan.conf"
2020-03-22T12:34:29.570230 [TRACE] Debug output enabled.
2020-03-22T12:34:29.572242 [INFORMATION] Loaded server certificate from: "/etc/ssl/certs/ssl-cert-snakeoil.pem"
2020-03-22T12:34:29.572436 [INFORMATION] Loaded server private key from: "/etc/ssl/private/ssl-cert-snakeoil.key"
2020-03-22T12:34:29.572478 [INFORMATION] Deriving pre-shared key from passphrase...
2020-03-22T12:34:29.575989 [INFORMATION] Setting core logging level to: trace.
2020-03-22T12:34:29.576018 [DEBUG] Opening core...
2020-03-22T12:34:29.576039 [INFORMATION] Enabling pre-shared key authentication.
2020-03-22T12:34:29.576052 [INFORMATION] Starting FSCP server...
2020-03-22T12:34:29.600974 [IMPORTANT] Core set to listen on: [::]:12000
2020-03-22T12:34:29.601014 [INFORMATION] Building CA store...
2020-03-22T12:34:29.601088 [IMPORTANT] Restricting VPN traffic on: eth0
2020-03-22T12:34:29.601102 [INFORMATION] FSCP server started.
2020-03-22T12:34:29.601682 [ERROR] Operation not permitted

root@srv:~# echo $?
1

Of course, you can start freelan with strace to find it:

root@srv:~# freelan -f -d -c /etc/freelan/freelan.conf
...
access("/dev/net/tap", F_OK)            = -1 ENOENT (No such file or directory)
mknod("/dev/net/tap", S_IFCHR|0600, makedev(10, 200)) = -1 EPERM (Operation not permitted)

A source of error would be helpfully. For exmaple "can not open device /dev/net/tap". Or a source file name and line number, may be only with option --debug.

Similar in #216 where SIOCSIFTXQLEN can not set. It ends with:

2020-03-22T12:48:55.504637 [INFORMATION] FSCP server started.
2020-03-22T12:48:55.520067 [ERROR] Operation not permitted

[s-vincent]

Hi and thanks for report.

Agree we should add some more explicit error message for system calls.