Skip to main content

what does /dev/null 2>&1 command do?

what does /dev/null 2>&1 command do ?
or
What does > /dev/null 2>&1″ mean?
I was running some CGI for disk formatting and during this process some warning messages were coming on screen; even though I was duplicating standard out file pointer to some temporary file pointer. It was not redirecting standard error messages to this temporary file. Searched on google, but was not able to hit google with right keyword. Got this answer of using /dev/null 2>&1.
Here is explanation,

In Linux There are three standard file descriptors, Standard In (STDIN, file descriptor 0), Standard Output (STDOUT, file descriptor 1) and Standard Error (STDERR, file descriptor 2). /dev/null is the null device, which is like "write only memory". > will write to the specified file (overwriting its contents) and >> will append to the specified file.

> /dev/null 2>&1 redirect both output and error to /dev/null
> /file 2>&1 redirect both output and error to /file

Explanation:
> redirects output to /dev/null
2>&1 redirect error to where > is redirected
So error also gets redirected to /dev/null

“> /dev/null” will redirect STDOUT to a BLACK HOLE

“2 > &1” will redirect STDERR to STDOUT which in turn is redirected to a BLACK HOLE

Comments

Popular posts from this blog

Dotnet, .Net 3.5, 2.0, C# Interview Questions

Few questions on dotnet, C# 2.0, 3.5 On Object oriented concepts 1)What is inheritance with e.g 2)What is polymorphism -function overloading -Function overriding -virtual keyword use -Static keyword and use -Abstract classes -Interface -Object 3)What is threading and how do we use in realtime application(cognizant) 4)What is threadpooling, lock, monitor(write code sample) 5)Architecture of current project 6)Session state, diffrent types of state management. 7)What is Application_Start, how it works. 8)Type of authentication in asp.net 9)How to configure ASP.NET application. 10) What is Impersonation. 11) What is WebService, WSDL, UDDI, Discovery, asmx files. 12) How to implement WebService and use it. 13) When to use WebServices. 14) WPF, how to implement(BOA) 15) Testing concvepts. 16) Test attributes 17) Flow of Automation Test Method execution 18) Features of dotnet 3.5 19) CLR, garbage collection 20) Finally block 21) Manifest, Metadata, MSIL 22) Assemblies, Type of assemblies, str...

Linux SMB write performance With Simple Tips

SMB write performance can be increased by Tuning the buffer cache. The secret to good performance is to keep as much of the data in memory for as long as is possible. Writing to the disk is the slowest part of any filesystem. If you know that the filesystem will be heavily used, then you can tune this process for Linux Samba. writing out dirty blocks to the disk until the filesystem buffer cache is 80 percent full (80). default is 40%, source = http://tldp.org/LDP/solrhe/Securing-Optimizing-Linux-RH-Edition-v1.3/chap29sec287.html by writing echo 80 > /proc/sys/vm/dirty_ratio I am getting around 2MB increase while write operation, tested in Xp. I have tried with this single option, as the ref source is for linux 2.2 and we are using 2.6 kernel. we can try out Linux General Optimization suggested at http://tldp.org/LDP/solrhe/Securing-Optimizing-Linux-RH-Edition-v1.3/gen-optim.html Tried with smb.conf, I am getting around 1MB gain while read and write. socket options = TCP_NODELAY I...

ahsec results 2008 | www.ahsec.nic.in

The official website of assam higher secondary education council Results of Assam is down seems they are uploading results , direct link to check ahsec results 2008 is http://resultsassam.nic.in/index.asp You can find results of AHSEC at the link above. current page The Website www.ahsec.nic.in Designed Developed & Hosted by NIC, Assam State Centre, Guwahati is down for result uploading. keep checking this page, I will update as soon as news comes. All the best to AHSEC - assam higher secondary education council students. Direct links http://assam.nic.in/ www.ahsec.nic.in http://resultsassam.nic.in/