How to translate error number to ‘errno’ constant

troubleshootingunix

Suppose I have an application running on a UNIX box that is failing with a system error status of '13'. Now, I can easily look up this value in errno.h, to find out that it is a permission-denied problem.

> grep -w 13 /usr/include/errno.h
#define EACCES  13      /* Permission denied                    */

Is there a simpler command to retrieve this information? I'd like to be able to run something like this:

> lookuperror 13
EACCES (Permission denied)

Instead of grepping system header files. Does such a command/program exist?

Update: As pointed out in the answers below, the strerror() system call returns this information. Are there any UNIX operating systems that ship with an executable utility that makes this system call, or do I need to write my own program to do it?

Best Answer

I use to do

perl -MPOSIX -e 'print strerror($ARGV[0])."\n";' 13

You can just put the Perl code in a file and have it in the path.
Of course it can be done using C as well

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SSH – How to Change Private Key Passphrase

To change the passphrase on your default key:

$ ssh-keygen -p

If you need to specify a key, pass the -f option:

$ ssh-keygen -p -f ~/.ssh/id_dsa

then provide your old and new passphrase (twice) at the prompts. (Use ~/.ssh/id_rsa if you have an RSA key.)

More details from man ssh-keygen:

[...]
SYNOPSIS
    ssh-keygen [-q] [-b bits] -t type [-N new_passphrase] [-C comment]
               [-f output_keyfile]
    ssh-keygen -p [-P old_passphrase] [-N new_passphrase] [-f keyfile]
[...]
     -f filename
             Specifies the filename of the key file.
[...]
     -N new_passphrase
             Provides the new passphrase.

     -P passphrase
             Provides the (old) passphrase.

     -p      Requests changing the passphrase of a private key file instead of
             creating a new private key.  The program will prompt for the file
             containing the private key, for the old passphrase, and twice for
             the new passphrase.
[...]

Windows – Whence for Windows

On my Vista laptop if I type "where java.exe" from the command prompt it gives me the location of java.exe.

Hope this helps.

Best Answer

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SSH – How to Change Private Key Passphrase

Windows – Whence for Windows

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