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License: see COPYING

Source code: https://github.com/libssh2/libssh2

Web site source code: https://github.com/libssh2/www

Installation instructions are in docs/INSTALL

To build libssh2 you will need CMake v3.7 or later [1] and one of the following cryptography libraries:

  • OpenSSL
  • wolfSSL
  • Libgcrypt
  • WinCNG
  • mbedTLS

Getting started

If you are happy with the default options, make a new build directory, change to it, configure the build environment and build the project:

  cmake -B bld
  cmake --build bld

Use this with CMake 3.12.x or older:

  mkdir bld
  cd bld
  cmake ..
  cmake --build .

libssh2 will be built as a static library and will use any cryptography library available. The library binary will be put in bin/src, with the examples in bin/example and the tests in bin/tests.

Customising the build

You might want to customise the build options. You can pass the options to CMake on the command line:

cmake -D= ..

The following options are available:

  • LINT=ON

    Enables running the source code linter when building. Can be ON or OFF. Default: OFF

  • BUILD_STATIC_LIBS=OFF

    Determines whether to build a libssh2 static library. Can be ON or OFF. Default: ON

  • BUILD_SHARED_LIBS=OFF

    Determines whether to build a libssh2 shared library (.dll/.so). Can be ON or OFF. Default: ON

  • CRYPTO_BACKEND=

    Chooses a specific cryptography library to use for cryptographic operations. Can be OpenSSL (https://www.openssl.org), Libgcrypt (https://www.gnupg.org/), WinCNG (Windows Vista+), mbedTLS (https://tls.mbed.org/) or blank to use any library available.

    CMake will attempt to locate the libraries automatically. See [2] for more information.

  • ENABLE_ZLIB_COMPRESSION=ON

    Use zlib (https://zlib.net/) for payload compression. Can be ON or OFF. Default: OFF

  • ENABLE_DEBUG_LOGGING=ON

    Enable the libssh2_trace() function for showing debug traces. Can be ON or OFF. Default: OFF in Release, ON in Debug

  • CLEAR_MEMORY=OFF

    Disable secure zero memory before freeing it (not recommended). Can be ON or OFF. Default: ON

Build tools

The previous examples used CMake to start the build using:

cmake --build .

Alternatively, once CMake has configured your project, you can use your own build tool, e.g GNU make, Visual Studio, etc., from that point onwards.

Tests

To test the build, run the appropriate test target for your build system. For example:

  cmake --build . --target test

or

  cmake --build . --target RUN_TESTS

How do I use libssh2 in my project if my project does not use CMake?

If you are not using CMake for your own project, install libssh2

  cmake <libssh2 source location>
  cmake --build .
  cmake --build . --target install

or

  cmake --build . --target INSTALL

and then specify the install location to your project in the normal way for your build environment. If you do not like the default install location, add -DCMAKE_INSTALL_PREFIX=<chosen prefix> when initially configuring the project.

How can I use libssh2 in my project if it also uses CMake?

If your own project also uses CMake, you do not need to worry about setting it up with libssh2's location. Add the following lines and CMake will find libssh2 on your system, set up the necessary paths and link the library with your binary.

find_package(libssh2 REQUIRED CONFIG)
target_link_libraries(my_project_target libssh2::libssh2)

You still have to make libssh2 available on your system first. You can install it in the traditional way shown above, but you do not have to. Instead you can build it, which will export its location to the user package registry [3] where find_package will find it.

You can even combine the two steps using a so-called 'superbuild' project [4] that downloads, builds and exports libssh2, and then builds your project:

include(ExternalProject)

ExternalProject_Add(
    libssh2
    URL <libssh2 download location>
    URL_HASH SHA256=<libssh2 archive SHA256>
    INSTALL_COMMAND "")

ExternalProject_Add(
    MyProject DEPENDS libssh2
    SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/src
    INSTALL_COMMAND "")

[1] https://www.cmake.org/cmake/resources/software.html [2] https://www.cmake.org/cmake/help/v3.0/manual/cmake-packages.7.html [3] https://www.cmake.org/cmake/help/v3.0/manual/cmake-packages.7.html#package-registry [4] https://blog.kitware.com/wp-content/uploads/2016/01/kitware_quarterly1009.pdf