What is Dev Null in cron?
/dev/null is a black hole where any data sent, will be discarded. 2 is the file descriptor for Standard Error. > is for redirect. & is the symbol for file descriptor (without it, the following 1 would be considered a filename) 1 is the file descriptor for Standard Out.
What does it mean Dev null 2 >& 1?
2>&1 redirects standard error to standard output. &1 indicates file descriptor (standard output), otherwise (if you use just 1 ) you will redirect standard error to a file named 1 . [any command] >>/dev/null 2>&1 redirects all standard error to standard output, and writes all of that to /dev/null .
How do I redirect cron to Dev Null?
You can easily suppress output of any cronjob by redirecting output to /dev/null. You can do this by appending >/dev/null 2>&1 to cronjob, for which you want to suppress output. This is more useful for the cron jobs running wget command. I have a cron job with wget run every minute.
What is Dev Null?
/dev/null in Linux is a null device file. This will discard anything written to it, and will return EOF on reading. This is a command-line hack that acts as a vacuum, that sucks anything thrown to it.
How do you use Dev Null?
You write to /dev/null every time you use it in a command such as touch file 2> /dev/null. You read from /dev/null every time you empty an existing file using a command such as cat /dev/null > bigfile or just > bigfile. Because of the file’s nature, you can’t change it in any way; you can only use it.
How do you read Dev Null?
What happens when you write to Dev Null?
Whatever you write to /dev/null will be discarded, forgotten into the void. It’s known as the null device in a UNIX system.
Do cron jobs run when not logged in?
1 Answer. cron is a process which deals with scheduled tasks whether you are logged in or not. It is not necessary to have a screen or tmux session running since the cron daemon will execute the scheduled tasks in separate shells.
How does Dev Null work?
/dev/null is a special type file known as a character device file. This means that the file acts like a device that is unbuffered and can accept streams of data. Any data written to /dev/null is discarded. However, the write operation will return successful.
Can I Tail Dev Null?
To answer your question under what circumstances tail -f /dev/null might finish and therefore continue to the next line in something like a shell script: /dev/null (as with everything in Linux) is a file. When executing tail onto any file, the file must be opened using a filedescriptor.
Why do we need dev Null?
The null device is typically used for disposing of unwanted output streams of a process, or as a convenient empty file for input streams. This is usually done by redirection. The /dev/null device is a special file, not a directory, so one cannot move a whole file or directory into it with the Unix mv command.
Why is CRON not emailing me from/dev/null?
With everything redirected to null, there is no output and hence cron will not email you. Show activity on this post. /dev/null is a device file that acts like a blackhole. Whatever that is written to it, get discarded or disappears.
What does >/dev/null mean in C++?
2>&1 means a redirection of the chanel 2 (stderr) to the chanel 1 (stdout). Both outputs are now on the same chanel (1). >/dev/null: means that the standard output (and the standard error output) is sent to /dev/null. /dev/null is a special file: Data written to a null or zero special file is discarded.
What does >/dev/null 2>&1 do?
Therefore >/dev/null 2>&1 redirects the output of your program to /dev/null. Include both the Standard Error and Standard Out. Much more information is available at The Linux Documentation Project’s I/O Redirection page.
What is a null device in crontab?
The null device is a device file that discards all data written to it. Then stderr is then being redirected into stdout ( 2>&1 ), therefore, both stdout and stderr will go to /dev/null So placing this at the end of a crontab job will suppress all output and errors from the command.