vb.net barcode component TAKING CONTROL OF THE SYS TEM in Java

Creating Code 39 Extended in Java TAKING CONTROL OF THE SYS TEM

What if you want to start a command running in a terminal window, but then want to close that terminal window As soon as you close the window, any processes started within it are also closed. Try this now type gcalctool at the prompt to start the Calculator application and then quit the terminal window. To get around this, you can use the nohup command. This stands for no hangup, and in simple terms, it tells the command you specify to stick around, even after the process that started it has ended (technically, the command is told to ignore the SIGHUP signal). However, commands run via nohup can still be killed. To use nohup, simply add it before the command, for example: nohup unzip myfile.zip If the command requires sudo or gksu powers, add either of these after the nohup command. Any command output (including error messages) is sent to the file nohup.out, which you can then view in a text editor. Note that if you run a command via nohup using sudo or gksu, the nohup.out file will have root privileges. If that s the case, you will also have to delete the nohup.out file via sudo before you can use nohup again as an ordinary user, because otherwise, nohup will be unable to overwrite the root-owned nohup.out.

Summary

This chapter has covered taking complete control of your system. We ve looked at what processes are, how they re separate from programs, and how they can be controlled or viewed using programs such as top and ps. In addition, we explored job management under BASH. You saw that you can stop, start, and pause programs at your convenience. In the next chapter, we ll take a look at several tricks and techniques that you can use with the BASH shell to finely hone your command-line skills.

he BASH shell is the product of many years of development work by a lot of people. It comes from the old days of Unix and was an important step in computer software evolution. It s a program that retains complete simplicity, yet packs in more features than most users could ever hope to use. One of the best things about the shell is its sheer power. If you ever wonder if you can do a task differently (and more efficiently), you ll probably find that one of the many BASH developers has implemented a method to do so. Once you learn these techniques, you ll find you can whiz around the shell at blinding speed. It s just a matter of exploring the far reaches of the shell, and that s what you ll do in this chapter. Hold onto your hats, because it s an exciting ride!

The Tab key is your best friend when using the shell, because it will cause BASH to automatically complete whatever you type. For example, if you want to run Ubuntu s web browser, you can enter firefox at the command line. However, to save yourself some time, you can type fir, and then press Tab. You ll then find that BASH fills in the rest for you. It does this by caching the names of the programs you might run according to the directories listed in your $PATH variable (see 13). Of course, autocompletion has some limitations. On my Ubuntu test system, typing loc didn t autocomplete locate. Instead, it caused BASH to beep. This is because on a default Ubuntu installation, there is more than one possible match. Pressing Tab again shows those matches. Depending on how much you type (how much of an initial clue you give BASH), you might find there are many possible matches. In this case, the experienced BASH user simply types another letter, which will be enough to distinguish the almost-typed word from the rest, and presses Tab again. With any luck, this should be enough for BASH to fill in the rest.