hello , 20 days ago, I had tried to install the gcc-master.zip packet, but failed, so I deleted the file I have installed, carelessly . two days ago I have the gcc-7 installed, there is a problem as followed: tom@tom-Inspiron-7447:~$ gcc -o test test.c gcc: error trying to exec 'cc1': execvp: No such file or directory tom@tom-Inspiron-7447:~$ gcc-7 -o test test.c tom@tom-Inspiron-7447:~$ ./test Hello world! so I want to completely delete the documents installed, "version 8.0.0", and set gcc to version 7, I have done some orders as follow tom@tom-Inspiron-7447:/usr/local/bin$ sudo update-alternatives --remove-all gcc tom@tom-Inspiron-7447:/usr/local/bin$ sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-7 70 update-alternatives: using /usr/bin/gcc-7 to provide /usr/bin/gcc (gcc) in auto mode tom@tom-Inspiron-7447:/usr/local/bin$ gcc -v Using built-in specs. COLLECT_GCC=gcc Target: x86_64-pc-linux-gnu Configured with: ./configure Thread model: posix gcc version 8.0.0 20170912 (experimental) (GCC) tom@tom-Inspiron-7447:/usr/local/bin$ sudo update-alternatives --config gcc There is only one alternative in link group gcc (providing /usr/bin/gcc): /usr/bin/gcc-7 Nothing to configure. tom@tom-Inspiron-7447:/usr/local/bin$ gcc -v Using built-in specs. COLLECT_GCC=gcc Target: x86_64-pc-linux-gnu Configured with: ./configure Thread model: posix gcc version 8.0.0 20170912 (experimental) (GCC) The orders did not work, I don't know how to do it ,would you give me any advice.