Sharing Files

A Safe Environment for Multiple Users Unix systems have multiple users – and a permissions system that lets each user share or protect their files. This unique system has some odd twists. For example, did you know that, to rename or remove a file, you need write permission for the directory that the file is …

Permissions

What are files? As we’ve discussed before, files are globs of data, in either text or binary form. File names can be up to 256 characters long with “-“, “_”, and “.” characters along with letters and numbers. When you do a long file listing, you see 10 characters on the left that indicate file …

Filesystems

The Filesystem Tree The Unix and Linux filesystem is based on the Filesystem Heirarchy Standard (FHS). (You can research it at http://www.pathname.com/fhs/ .) There are no C: drives, D: drives or any other lettered drives. Instead, all disks are mounted into a common filesystem tree. You can even mount other computers into this tree. Everyone …

Links

The ln Command This command creates either hard links or soft (sym) links; soft links are similar to Windows shortcuts. Hard links are a new concept to Windows users; they effectively put the exact same file in more than one location. Symlinks are very similar (but not identical) to shortcuts. By default, the ln command …

Utilities: SSH

ssh Repeat after me: “I will never use Telnet unless I have a direct serial connection to a router.” Got it? Telnet is disastrously unsafe; it transmits your user name and password in clear text. In Windows, you will need a SSH client program. Consider putty, for instance. In Unix, SSH is built into the …

Utilities: Mail

Mail The general syntax for command-line mail is: mail [-s subject] [-c CC to] [-b BCC to] some_address@some.host The command mail issued by itself opens a mail session, prints out message headers and lets you read, page through messages and delete them.   Reading Mail Start reading your messages by issuing the command: print or …

Utilities: FTP

In the world of Windows, we’re accustomed to installing programs for specific functions, like FTP, email, and Secure Shell connections. With Linux and Unix, utilities are provided with the operating system, and are easily invoked from the command line. ftp The File Transfer Protocol (FTP) utility is an easy way to transfer files between computers.  All …