Having downloaded archives of Sage, Firefox, and Thunderbird from their respective websites on Trisquel 6.0, neither clicking the appropriate shell script nor executing a command to run the programs will open them. Looking at the files' permissions, they are indeed executable.Edit: Firefox and Thunderbird have now mysteriously started working; Sage, however, remains inoperable. Having downloaded it from the first link on this page, extracted it to my desktop (where Firefox and Thunderbird run just fine), opened the folder in the terminal and run the command sage (as there is an executable by that name in the folder) I receive the error: bash: sage: command not found. Yet ls -l  shows that the files are known to exist and be executable.Edit #2: I only thought Firefox and Thunderbird were working. I was actually running the versions I already have installed. Running Firefox and/or Thunderbird with ./[executable] gives the error libxul.so: cannot open shared object file: No such file or directory Couldn't load XPCOM.
Why can't I run programs extracted from an archive?
software installation;executable
The first thing to check after extracting a program from an archive is the permissions (chmod a+x ./sage), but if that was the problem, the error message would be permission denied and not command not found.Give your description opened the folder in the terminal and run the command, it's likely that you ran the command sage expecting to execute the program with this name in the current directory. Unix doesn't work like this: the shell only looks for programs in the directories listed in the PATH environment variable. It doesn't search the current directory implicitly first. To run a program in the current directory, you need to type its path:./sageIf you want to run the program without specifying a path, you need to install it in a directory in your $PATH (typically /usr/local/bin or ~/bin). It's often convenient to leave the executable with the other files from the application and make a symbolic link to it in a directory in $PATH:ln -s /path/to/sage-5.9/sage ~/bin/or if you're already in the directory containing the sage binary:ln -s $PWD/sage ~/bin/If you've just added a program to a directory in your PATH and your shell still complains that the command is not found, it may be because you tried before and your shell has kept the not found information in a cache. Run hash -r to rebuild the cache and try again. The next time you start a shell, this won't be a problem any more, because the cache isn't saved between runs of the shell.If you execute a file that is present, with a specified path, and you get the command not found error message, it may be because you don't have the right loader. This can happen if you downloaded a binary that is supported by your CPU and kernel but you don't have the required userland support (no libraries). This can also happen if the program is a script whose shebang line refers to an interpreter that isn't present on your system (though typical shells give a bad interpreter message rather than command not found in this case).