Question

I downloaded and installed the latest libssh2 from their website into the location /usr/src/libssh2-1.4.0

I was trying to build one of the example programs (ssh2.c) that is available in the example directory. When I compiled with make from /usr/src/libssh2-1.4.0/example as

make ssh2

, it compiled and ran quite fine. I then copied the program ssh2.c to a different path (~/Projects/precious/) and issued the command

gcc -g -I/usr/src/libssh2-1.4.0/src -I/usr/src/libssh2-1.4.0/include -I/usr/src/libssh2-1.4.0/src/obj ssh.c -o ssh -lssh2 -ldl -lnsl -lresolv -lcrypto -lssl -lz 

When I am trying to run the program, it greets me with the following message

./ssh: symbol lookup error: ./ssh: undefined symbol: libssh2_session_handshake

I also tried to compile it simply as

g++ -g ssh.c -o ssh -lssh2

The response is all the same.

I also tried compiling as

gcc -DHAVE_CONFIG_H      -g -O2  -I/usr/src/libssh2-1.4.0/src -I/usr/src/libssh2-1.4.0/include -I/usr/src/libssh2-1.4.0/src/obj -c -o ssh.o ssh.c 
libtool --tag=CC --mode=link gcc  -g -O2   -o ssh  ssh.o /usr/local/lib/libssh2.la

but without any luck. Please suggest

Answer 1

I suspect that your libssh2 package that you’ve built by hand is a different version (probably newer) than the one installed on your system. And your link line is trying to use the one installed on the system, which doesn’t have the libssh2_session_handshake function in it. Try this line:

gcc -g -L/usr/local/lib -I/usr/src/libssh2-1.4.0/src -I/usr/src/libssh2-1.4.0/include -I/usr/src/libssh2-1.4.0/src/obj ssh.c -o ssh -lssh2 -ldl -lnsl -lresolv -lcrypto -lssl -lz 

or maybe this one:

gcc -g -L/usr/src/libssh2-1.4.0/src/obj -I/usr/src/libssh2-1.4.0/src -I/usr/src/libssh2-1.4.0/include -I/usr/src/libssh2-1.4.0/src/obj ssh.c -o ssh -lssh2 -ldl -lnsl -lresolv -lcrypto -lssl -lz 

The important thing is to get the -L flag pointing to the path where your compiled library is located.