Picture this scenario. You are trying to copy a large file from one directory to another or one system to another through command line. As you probably know, you will not see any indication of copy task if you're using 'cp' command. You'll just see an empty screen. You can't be sure whether the copy process is going on or not, until the copy process is completed. In such cases, you can use pv command to monitor the progress of data. The pv, acronym of pipe viewer, command allows a user to see the progress of data through a pipeline, by giving the following information:
- total time elapsed,
- percentage completed (with progress bar),
- current throughput rate,
- total data transferred,
- and ETA.
In this brief tutorial, we will see how and where to use pv command to monitor the progress of data in Unix-like systems.
Monitor The Progress Of Data Through A Pipe Using 'pv' Command
Most modern Linux distributions comes pre-installed with pv command. Just in case if it is not installed already, you can install it by running the following command from your Terminal depending upon the Linux distribution you use.
On Arch Linux, Antergos, Manjaro Linux:
$ sudo pacman -S pv
On RHEL, CentOS, Fedora:
$ sudo yum install pv
$ sudo dnf install pv
On Debian, Linux Mint, Ubuntu:
$ sudo apt-get install pv
On SUSE, openSUSE:
$ sudo zypper in pv
Now, we have installed pv. Let me show you some examples.
pv command usage
Look at the output of the following command:
$ cp CentOS7.iso Downloads/
This command copies CentOS 7 ISO image to Downloads directory in my local system. As you see in the above output, it doesn't show any progress bar. You will only see the cursor blinking. We don't know how much time the copy process will take. This could be annoying sometimes as we don't see any sign of when this command will complete. This is where pv command comes in help. The pv command will show you the progress of Linux commands, and show you when the Linux command will complete. So, you can leave the Terminal and do some other tasks and come back when the task is done.
Now, let us do the same with pipe viewer (pv), and see what is the output.
$ pv CentOS7.iso > Downloads/centos.iso
See, you get the difference? Like I said, the pv command displays total time elapsed, percentage completed (with progress bar), current throughput rate, total data transferred, and ETA.
Let me give you some more examples.
We can limit the data transfer rate using -L switch as shown in the below example.
$ pv -L 2m CentOS7.iso > Downloads/centos.iso
The above command will limit the data transfer rate to 2MB per second. Look at the following output.
If you have multiple files or directories you can use pv with tar command as shown below:
$ tar c Notebooks/ | pv | tar x -C Documents/
The above command will compress the directory Notebooks, and copy it to Documents directory and finally extract the contents.
Here is another example. This command will will create an archive of CentOS7.iso file and save it in the current working directory.
$ pv CentOS7.iso | zip > centos.zip
You can also use pv with dd command to copy files between directories like below. This command copies CentOS7.iso file from the current directory to Downloads directory.
$ dd if=CentOS7.iso | pv | dd of=Downloads/centos7.iso
Another useful command to display the progress of data is dialog. We can use it along with pv command to show the progress of data like below.
$ tar -czf - Official/ | (pv -n > mybackup.tgz) 2>&1 | dialog --gauge "Compressing files, please wait..." 10 70 0
For more details, refer the man pages.
$ man pv
Also, check our previous guide to quickly transfer large files between between two remote systems over Network using netcat, tar, and pv commands in Linux and Unix operating systems.
And, that's all for now. Hope this helps. I will be soon here with another useful guide. If you find our articles helpful, please share them on your social, professional networks and support OSTechNix.
More good stuffs to come. Stay tuned!