I encountered an input/output bug in R in Linux system. The symptom is that input and output are not displayed in the terminal and the warning message "An unusual circumstance has arisen in the nesting of readline input. Please report using bug.report()" is shown. I found that though input and output are not displayed, you can still interact with the underlying R session. A safe way is to save the R workspace, quit the R session, open a new R session and load in the saved workspace. To save the R workspace, just type in save.image('ws_name') in the console, where ws_name is the name of the workspace. Notice that you will not see anything happen on the console, so you have to make sure that you do not make any mistake typing in the command. To quit the R session after saving the workspace, you can type in 'q('no')' in the console. Similarly, you won't see anything in the console, so make sure you do not make any mistake. Now can open a new R session, and then load in the saved workspace.