nslookup : $ nslookup www.google.com Server: 127.0.0.1 ... dig : $ dig +noall +answer www.google.com www.google.... host $ host www.google.com www.google.com has addres... About the use of reverse DNS from webdnstools.com : Many things use reverse DNS. An example is anti-spam email software. Before delivering an email, it is common for anti-spam software to perform a reverse DNS lookup on the IP address of the source mail server. It then checks that the reverse DNS entry matches the SPF record provided by the name server of the source email domain. If it does not match, it may flag the email as spam.

From Version Control with Subversion, Chapter 4. Branching and Merging In Subversion, a global revision number N names a tree in the repository: it's the way the repository looked after the N th commit. It's also the name of an implicit changeset: if you compare tree N with tree N-1 , you can derive the exact patch that was committed. For this reason, it's easy to think of revision N as not just a tree, but a changeset as well. If you use an issue tracker to manage bugs, you can use the revision numbers to refer to particular patches that fix bugs—for example, “this issue was fixed by r9238.” Somebody can then run svn log -r 9238 to read about the exact changeset that...

According to MSDN : On Windows 7 and on Windows Server 2008 R2 with the Wireless LAN Service installed, the operating system installs a virtual device if a Hosted Network capable wireless adapter is present on the machine. This virtual device normally shows up in the "Network Connections Folder" as "Wireless Network Connection 2" with a Device Name of "Microsoft Virtual WiFi Miniport adapter" if the computer has a single wireless network adapter. This virtual device is used exclusively for performing software access point (SoftAP) connections. The lifetime of this virtual device is tied to the physical wireless adapter. If the physical wireless adapter is disabled, this virtual device will be removed as well. On Windows 7, there's no UI to start or stop SoftAP....

Use the shortcut CTRL+ALT+T to bring up a terminal in Ubuntu.

IFS : The Internal Field Separator that is used for word splitting after expansion and to split lines into words with the read builtin command. The default value is "<space><tab><newline>". $ echo "$IFS" | cat -vte ^I$ $

First, the test command that sleeps random number of seconds ( sleeper.sh ): #!/bin/bash stime=$[$RANDOM % 20] sleep $sti... As comparison, synchronous pipe code: #include <sys/wait.h> #include <stdio.h> #in... Asynchronous pipe code: #include <sys/wait.h> #include <stdio.h> #in...

Example 1, from the pipe man page. The parent then writes the string contained in the program's command-line argument to the pipe, and the child reads this string a byte at a time from the pipe and echoes it on standard output. #include <sys/wait.h> #include <stdio.h> #in... Example 2, child execs command given at the command line, then writes to stdout (of child), which is piped to parent. Parent reads from pipe and writes to stdout (of parent). #include <sys/wait.h> #include <stdio.h> #in...

execl takes the full path name of the command and variable length of arguments terminated by NULL: execl("/bin/ls", "/bin/ls", "-r", "-t", "-l", NULL... where the second argument is argv[0] , but can be any string! execlp will try to find the command from $PATH , so full path to command is not needed: execl("ls", "ls", "-r", "-t", "-l", NULL); execv is the equivalent of execl , except that the arguments are passed in as a NULL terminated array: char *args[] = {"/bin/ls", "-r", "-t", "-l", NULL ... execvp is the equivalent of execvl , excep that the arguments are passed in as a NULL terminated array: char *args[] = {"ls", "-r", "-t", "-l", NULL }; ...

Start gdb with the executable and coredump: $ gdb <path to executable> core While in the debugger, use the following commands: (gdb) where ("shows a summary of the stack") ... Example debug session from Debugging Under Unix: gdb Tutorial : Use backtrace (or bt ) to see the callstack: (gdb) backtrace #0 Node<int>::next (this=0x0) ... Inspect the value of item_to_remove at address 0xffbef014 (the value is 1): (gdb) x 0xffbef014 0xffbef014: 0x00000001 (g... Note: The program must be compiled with the debug switch -g in order to see the source code. More resources: Linux software debugging with GDB Debugging with gdb

My program core dumped but there was no core file. The problem was that the core file size was 0: $ ulimit -a core file size (blocks, -c... Use ulimit to enable it: $ sudo bash # ulimit -c unlimited Actually, you can update the limit for yourself without root. You can put the ulimit command in .bashrc .