Linux vs UNIX as Operating Systems - Essay Example

and number] in format: 12 May 2002] Linux vs HP-UNIX UNIX as an operating system is uniquely exceptional through its file system and the ability to coordinate the naming of resources as well as accessing the same resources. An idea was therefore adopted to "design a network-level protocol, called 9P, to enable machines to access files on remote systems." (Pike et al) Bell Labs As UNIX worked toward being a reputable file system and operating system, but, as this type of file system and operating system becomes redundant another more powerful user friendly operating system called Linux. Kernel Many of the new operating systems tend to implement two classes of processes. In the older versions of UNIX (pre- 8 ), these included normal UNIX-style processes and light-weight kernel threads. In version 9 (Plan 9) the operating system provides a single class of process and allows fine control of sharing resources such as resources like memory and file descriptors. "A single class of process is a feasible approach in Plan 9 because the kernel has an efficient system call interface and cheap process creation and scheduling." (Pike et al) Bell Labs: The kernel support for parallel programming in Plan 9 is a few hundred lines of portable code; a handful of simple primitives enable the problems to be handled cleanly at user level. Although the primitives work fine from C, they are particularly expressive from within Alef. The creation and management of slave I/O processes can be written in a few lines of Alef, providing the foundation for a consistent means of multiplexing data flows between arbitrary processes. (Pike et al) Bell Labs UNIX is a "multi-tasking OS, which means that there may be many programs and many programs and people using the same machine at the same time, by using the concept of a virtual machine". (Seth Noble, 2005) The kernel mechanisms in Linux are much more advanced to continue on with the multi-tasking OS that UNIX is and is described as: Linux's bottom half handlers were invented so that device drivers and other parts of the Linux kernel could queue work to be done later on. Figure 11.1 shows the kernel data structures associated with bottom half handling. Bottom Half Handling Figure 11.1: Bottom Half Handling Data Structures There can be up to 32 different bottom half handlers; bh_base is a vector of pointers to each of the kernel's bottom half handling routines. bh_active and bh_mask have their bits set according to what handlers have been installed and are active. If bit N of bh_mask is set then the Nth element of bh_base contains the address of a bottom half routine. If bit N of bh_active is set then the N'th bottom half handler routine should be called as soon as the scheduler deems reasonable. These indices are statically defined; the timer bottom half handler is the highest priority (index 0), the console bottom half handler is next in priority (index 1) and so on. Typically the bottom half handling routines have lists of tasks associated with them. For example, the immediate bottom half handler works its way through the immediate tasks queue (tq_immediate) which contains tasks that need to be performed immediately. (Rusling, David 1999) Shell The shell application inside the UNIX Plan9 system are set up for standard input and output connection to the editable text of the window with such features as its own private bitmap and multiplexed access to the keyboard, mouse and other graphical resources. The UNIX shell is commonly defined as the command line which provides the user interface for the actual operating system. By executing input commands, the shell will then execute those exact inputs. There are different shells that are available for Linux and is very much the same as UNIX in its description of how the shell application works. The following shells are available for Linux: Shell Name Developed by Where Remark BASH ( Bourne-Again SHell ) Brian Fox and Chet Ramey Free Software Foundation Most common shell in Linux. It's Freeware shell. CSH (C SHell) Bill Joy University of California (For BSD) The C shell's syntax and usage are very similar to the C programming language. KSH (Korn SHell) David Korn AT & T Bell Labs -- TCSH See the man page. Type $ man tcsh -- TCSH is an enhanced but completely compatible version of the Berkeley UNIX C shell (CSH). Tip: To find all available shells in your system type following command: $ cat /etc/shells Note that each shell does the same job, but each understand a different command syntax and provides different built-in functions. (LSST, n.d.) API The UNIX API still relies on the ISO POSIX-1 standard and relies on several tables and "is a source level API specification which has traditionally built upon the formal IEEE POSIX standards. It is vendor neutral and not tied to any particular implementation." (OpenGroup, 2004) The UNIX kernel provides various services to user programs by means of system calls which are defined as the API. Unix is a class with a well-defined set of methods. The API within the Linux environment is only a variation of UNIX and as such Linux is a kernel that implements the current standard for the UNIX API. Any program that is written for UNIX will compile and run on Linux and is backward compatible. The "core, though, works exactly like the core API for every version of UNIX." (Harvard, 2000) File Management The UNIX file system are organized in a hierarchical fashion very similar to the fashion in which many corporations are organized (a tree structure) and similar files are clustered into a directory which then have subdirectories. This is the same concept as what is found in the Windows X and Macintosh systems. At the base of file hierarchy is the root directory which is accessed by a designated single slash (/). There are certain major directories which are underneath the root directory (e.g. /usr, /home, /man, /tmp). These major directories contain further sub-directories such as /usr/bin/. This file structure can then get even more complex and extends even further into the subdirectory structure. The file system for Linux is similar to UNIX by the structure of how the file system hierarchy is devised, but, one of the most important features is that Linux supports many different file systems. In fact, Linux supports 15 file systems: "ext, ext2, xia, minix, umsdos, msdos, vfat, proc, smb, ncp, iso9660, sysv, hpfs, affs and ufs, and no doubt, over time more will be added." (Rusling, David 1999) Process Management The second major component of the kernel is the process management system. A process is really a single sequence of events with utilize memory and/or files. A process is then created by 'forking' a copy of the process being made. The only distinguishing factor in the processes is the parent process waiting for the child process to finish. There is a process hierarchy found in UNIX and is called the init which is loaded after the swapper process which the kernel creates after loading itself. The Linux system, being a multitasking operating system can have many processes running at one time. "Control is maintained in a 'preemtive' or 'timesliced' fashion. After a certain amount of time (in milliseconds) the operating system passes operation over from process 'a' to process 'b'. This also lets it maintain control and break out of rogue processes. Some other systems use a 'cooperative' system where eachprocess relinquishes control when it wants to (but what happens when it doesn't want to)." (Russel, John 2004) Memory Management The memory management system in UNIX decides which processes should reside (even partially) within the main memory and monitors the amount of available primary memory and may periodically write processes to a secondary device called the swap device to provide more space in primary memory. At a later time, the kernel reads the data from swap device back to main memory. (Bach, Maurice, n.d.) Memory management policies include: swapping which is easy to implement and has less system overhead; demand paging which offers greater flexibility The Linux memory management "subsystem is one of the most important parts of the operating system and contains the following: large address spaces, protection, memory mapping, fair physical memory allocation, shared virtual memory." (Rusling, David, 1999) Security There are many built-in security tools that are available with UNIX as well as patches that are necessary to keep the operating system fully secure. These network security tools include: Ipacl: forces all TCP and UDP packets to pass through an access control list facility Logdaemon: provides modified versions of rshd, rlogind, ftpd, rexecd, login and telnetd Portmap: a replacement for the standard portmap program that attempts to close all known holes in portmap This includes prevention of NIS password theft, prevention of unauthorized ypset commands and prevention of NFS file handle theft Rpcbind: offers access control and copious logging and allows host access control based on network addresses Sara: is a third generation UNIX-based security analysis tool that is based on the SATAN model SATAN: is a network security analyzer that scans systems connected to the network noting the existence of well known, often exploited vulnerabilities. Scanssh: scans networks for SSH servers and returns the connection string provided by the server Screend: provides a daemon and kernel modifications to allow all packets to be filtered based on source address, destination address, or any other byte or set of bytes in the packet Securelib: provides a replacement shared library from SunOS 4.1x systems that offers new versions of the accept, recvfrom, and recvmsg networking system calls TCP Wrappers: allows monitoring and control over who connects to a host through TFTP, EXEC, FTP, RSH, TELNET, RLOGIN, FINGEr and SYSTAT ports Xinetd: is a replacement for inetd and supports access control based on the address of the remote host and the time of access. There a many available tools for securing a Linux system, which includes: PGP and Public-key Cryptography SSL, S-HTTP and S/MIME IPSEC Implementations ssh (Secure Shell) and stelnet PAM (pluggable authentic modules) Cryptographic IP Encapsulation (CIPE) Kerberos Shadow Passwords "Crack" and "John the Ripper" CFS - Cryptographic File System and TCFS - Transparent Cryptographic File System X11, SVGA and display security SVGA GGI (Generic Graphics Interface project) Licensing UNIX licensing is broken down into the following configurations: Vendors of single-user desktop machines priced at about $10,000 will pay about $120 in royalties for Release 4.0, compared with the current $210 licensing fee. On a large minicomputer, vendors will pay between $1,650 and $3,300 for Release 4.0, compared with the current $2,860 fee. (New York Times, 2006) Licensing for Linux, on the other hand, is handled as a general public license and is not to be confused with shareware, as well as Linux is not in the public domain. The kernel is copyrighted as well as other software and parts of the kernel by their respective authors. Conclusion Through looking at the different aspects of both Bell's UNIX Plan9 and Linux both as operating systems and their feasibility in both a operating system and ability it is more than apparent that Linux is the natural progression from UNIX, but, as Bell Labs state they were in too deep with UNIX to fix it, but, based on the cost for licensing and ease of use it would be a wise decision to stop using UNIX as their operating system now and migrate toward Linux. Since Linux can work with any file system and is backward compatible to such file systems as UNIX it would not be a wasted progression as it would simply only take time in transferring files into the new file system hierarchy. Works Cited Bach, Maurice J. n.d. "Memory Management Policies: UNIX". 2006 Apr. 12 Noble, Seth B. "The UNIX Kernel". 2005. Expedition, Inc. 2006 Apr. 12 http://dataexpedition.com/sbnoble/Tips/kernel.html Harvard Education. "Is Linux UNIX" 2006 Apr. 12 Josey, Andrew. "API standards for Open Systems". 2003-2004. The Open Group. 2006 Apr. 12 Linux Shell Scripting Tutorial (LSST). N.D. "What is Linux Shell". 2006 Apr. 12 < http://www.freeos.com/guides/lsst/ch01sec07.html> Pike, Rob, Dave Presotto, Sean Dorward, Bob Flandrena, Ken Thompson, Howard Trickey, and Phill Winterbottom. "Plan 9 from Bell Labs." Bell Labs. Ed. Bell Laboratories. 2006. Bell Laboratories. 2006 Apr. 12 http://www.cs.bell-labs.com/sys/doc/9.html Russel, John W. (2004) "The Linux Kernel". 2006 Apr. 12 Read More