How started file in linux

Linux: How to know where a process was started and how it was started?

I was checking a Linux box and found a perl process running and taking a good share of cpu usage. With top, i could only perl in process name. When i pressed c, to view the command-line, it showed /var/spool/mail. Which does not make sense, since this is directory. My questions are: 1) Why did this happen? How this perl process could mask its command-line? 2) What is the most reliable way of finding out where and how a process was started? Thanks!

9 Answers 9

In most cases just running ps is usually sufficient, along with your favorite flags to enable wide output. I lean towards ps -feww , but the other suggestions here will work. Note that if a program was started out of someone’s $PATH , you’re only going to see the executable name, not the full path. For example, try this:

$ lftp & $ ps -feww | grep ftp lars 9600 9504 0 11:30 pts/10 00:00:00 lftp lars 9620 9504 0 11:31 pts/10 00:00:00 grep ftp 

It’s important to note that the information visible in ps can be completely overwritten by the running program. For example, this code:

int main (int argc, char **argv)

If I compile this into a file called «myprogram» and run it:

$ gcc -o myprogram myprogram.c $ ./myprogram & [1] 10201 

And then run ps , I’ll see a different process name:

$ ps -f -p 10201 UID PID PPID C STIME TTY TIME CMD lars 10201 9734 0 11:37 pts/10 00:00:00 foobar 

You can also look directly at /proc//exe , which may be a symlink to the appropriate executable. In the above example, this gives you much more useful information than ps :

$ls -l /proc/9600/exe lrwxrwxrwx. 1 lars lars 0 Feb 8 11:31 /proc/9600/exe -> /usr/bin/lftp 

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4 Ways to Create a Text File in Linux Terminal

In this Linux beginner series, you’ll learn various methods to create a file in Linux terminal.

In this Linux beginner series, you’ll learn various methods to create a text file in Linux terminal.

If you have used the desktop oriented operating system such as Windows, creating file is a piece of cake. You right click in the file explorer and you would find the option of creating new file.

Things won’t look the same when you are in a command line environment. There is no right click option here. So how do you create a file in Linux then? Let me show you that.

Create file in Linux command line

There are various ways of creating a new file in Linux terminal. I’ll show you the commands one by one. I am using Ubuntu here but creating files in Ubuntu terminal is the same as any other Linux distribution.

1. Create an empty file using touch command

One of the biggest usages of the touch command in Linux is to create a new empty file. The syntax is super simple.

If the file doesn’t exist already, it will create a new empty file. If a file with the same name exists already, it will update the timestamps of the file.

2. Create files using cat command

Another popular way of creating new file is by using the cat command in Linux. The cat command is mostly used for viewing the content of a file but you can use it to create new file as well.

You can write some new text at this time if you want but that’s not necessary. To save and exit, use Ctrl+D terminal shortcut.

If the file with that name already exists and you write new text in it using the cat command, the new lines will be appended at the end of the file.

3. Create new file using echo command

The main use of the echo command is to simply repeat (echo) what you type on the screen. But if you use the redirection with echo, you can create a new file.

To create a new file using echo you can use something like this:

echo "This is a sample text" > filename.txt

The newly created filename.txt file will have the following text: This is a sample text. You can view the file in Linux using cat or other viewing commands.

You are not obliged to put a sample text with echo. You can create an (almost) empty file using the echo command like this:

This will create a new file with just one empty line. You can check the number of lines with wc command.

4. Create a new file using a text editor like Nano or Vim

The last method in this series is the use of a text editor. A terminal-based text editor such as Emacs, Vim or Nano can surely be used for creating a new file in Linux.

Before you use these text editors, you should make sure that you know the basics such as saving an existing from the editor. Unlike the GUI tools, using Ctrl+S in the terminal won’t save the file. It could, in fact, send your terminal into a seemingly frozen state from which you recover using Ctrl+Q.

Let’s say you are going to use Vim editor. Make sure that you are aware of the basic vim commands, and then open a new file with it like this:

What’s your favorite command?

So, I just shared 4 different ways of creating a file in Linux. Personally, I prefer using touch for creating empty file and Vim if I have to edit the file. On a related note, you may want to learn about the file command in Linux that is helpful in determining the actual type of the file.

Which command do you prefer here? Please share your views in the comment section below.

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How to create a file in Linux from terminal window? [closed]

• touch /path/to/file for an empty file
• somecommand > /path/to/file for a file containing the output of some command.

 eg: grep --help > randomtext.txt echo "This is some text" > randomtext.txt 

UNIX is not a command line environment, but a family of (very different) OSes. That said: Yes, this should work on most Unices

touch will work in UNIX, because it’s a standard tool. The somecommand example will work because it uses standard syntax. The nano sample may not work because an editor named nano may not be installed (nano is not standardized). The standard editor is ed and could be used in place of nano , or you could use $EDITOR to use your user- or system-configured default text editor, if there is one.

Additionally, you could simply say >/path/to/file to create an empty file, even if you don’t have touch .

Create the file using cat

Now, just type whatever you want in the file:

When I tried cat /etc/systemd/system/sample.service , it said «no such file or directory» rather than creating a new sample.service file.

@TylerH cat /etc/systemd/system/sample.service prints the file to the console cat > /etc/systemd/system/sample.service redirects standard input to the file (which is why you need to close standard input by pressing control-d.

There are several possible solutions:

Create an empty file

touch file >file echo -n > file printf '' > file 

The echo version will work only if your version of echo supports the -n switch to suppress newlines. This is a non-standard addition. The other examples will all work in a POSIX shell.

Create a file containing a newline and nothing else

echo '' > file printf '\n' > file 

This is a valid «text file» because it ends in a newline.

Write text into a file

"$EDITOR" file echo 'text' > file cat > file file 

These are equivalent. The $EDITOR command assumes that you have an interactive text editor defined in the EDITOR environment variable and that you interactively enter equivalent text. The cat version presumes a literal newline after the \ and after each other line. Other than that these will all work in a POSIX shell.

Of course there are many other methods of writing and creating files, too.

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