So I was installing something (forgot what), and had problems with RCurl:

* installing *source* package ‘RCurl’ …
** package ‘RCurl’ successfully unpacked and MD5 sums checked
checking for curl-config… no
Cannot find curl-config
ERROR: configuration failed for package ‘RCurl’
* removing ‘/home/lenovo/R/x86_64-pc-linux-gnu-library/3.1/RCurl’
Warning in install.packages :
installation of package ‘RCurl’ had non-zero exit status

Solution was to do sudo apt-get install libcurl4-openssl-dev (found in a comment here).