Some Basic UNIX Commands
The UNIX operating system has for many years formed the backbone of the Internet, especially for large servers and most major university campuses. However, a free version of UNIX called Linux has been making significant gains against Macintosh and the Microsoft Windows 95/98/NT environments, so often associated with personal computers. Developed by a number of volunteers on the Internet such as the Linux group and the GNU project, much of the open-source software is copyrighted, but available for free. This is especially valuable for those in educational environments where budgets are often limited.
UNIX commands can often be grouped together to make even more powerful commands with capabilities known as I/O redirection ( < for getting input from a file input and > for outputing to a file ) and piping using | to feed the output of one command as input to the next. Please investigate manuals in the lab for more examples than the few offered here.
The following charts offer a summary of some simple UNIX commands. These are certainly not all of the commands available in this robust operating system, but these will help you get started.
Ten ESSENTIAL UNIX Commands
These are ten commands that you really need to know in order to get started with UNIX. They are probably similar to commands you already know for another operating system.| Command | Example | Description |
|---|---|---|
| 1. ls | ls ls -alF | Lists files in current directory List in long format |
| 2. cd | cd tempdir cd .. cd ~dhyatt/web-docs | Change directory to tempdir Move back one directory Move into dhyatt's web-docs directory |
| 3. mkdir | mkdir graphics | Make a directory called graphics |
| 4. rmdir | rmdir emptydir | Remove directory (must be empty) |
| 5. cp | cp file1 web-docs cp file1 file1.bak | Copy file into directory Make backup of file1 |
| 6. rm | rm file1.bak rm *.tmp | Remove or delete file Remove all file |
| 7. mv | mv old.html new.html | Move or rename files |
| 8. more | more index.html | Look at file, one page at a time |
| 9. lpr | lpr index.html | Send file to printer |
| 10. man | man ls | Online manual (help) about command |
Ten VALUABLE UNIX Commands
Once you have mastered the basic UNIX commands, these will be quite valuable in managing your own account.| Command | Example | Description |
|---|---|---|
| 1. grep <str><files> | grep "bad word" * | Find which files contain a certain word |
| 2. chmod <opt> <file> | chmod 644 *.html chmod 755 file.exe | Change file permissions read only Change file permissions to executable |
| 3. passwd | passwd | Change passwd |
| 4. ps <opt> | ps aux ps aux | grep dhyatt | List all running processes by #ID List process #ID's running by dhyatt |
| 5. kill <opt> <ID> | kill -9 8453 | Kill process with ID #8453 |
| 6. gcc (g++) <source> | gcc file.c -o file g++ fil2.cpp -o fil2 | Compile a program written in C Compile a program written in C++ |
| 7. gzip <file> | gzip bigfile gunzip bigfile.gz | Compress file Uncompress file |
| 8. mail (pine) | mail me@tjhsst.edu < file1 pine | Send file1 by email to someone Read mail using pine |
| 9. telnet <host> ssh <host> | telnet vortex.tjhsst.edu ssh -l dhyatt jazz.tjhsst.edu | Open a connection to vortex Open a secure connection to jazz as user dhyatt |
| 10. ftp <host> ncftp <host/directory> | ftp station1.tjhsst.edu ncftp metalab.unc.edu | Upload or Download files to station1 Connect to archives at UNC |
Ten FUN UNIX Commands
These are ten commands that you might find interesting or amusing. They are actually quite helpful at times, and should not be considered idle entertainment.| Command | Example | Description |
|---|---|---|
| 1. who | who | Lists who is logged on your machine |
| 2. finger | finger | Lists who is on computers in the lab |
| 3. ytalk <user@place> | ytalk dhyatt@threat | Talk online with dhyatt who is on threat |
| 4. history | history | Lists commands you've done recently |
| 5. fortune | fortune | Print random humerous message |
| 6. date | date | Print out current date |
| 7. cal <mo> <yr> | cal 9 2000 | Print calendar for September 2000 |
| 8. xeyes | xeyes & | Keep track of cursor (in "background") |
| 9. xcalc | xcalc & | Calculator ("background" process) |
| 10. mpage <opt> <file> | mpage -8 file1 | lpr | Print 8 pages on a single sheet and send to printer (the font will be small!) |
Ten HELPFUL UNIX Commands
These ten commands are very helpful, especially with graphics and word processing type applications.| Command | Example | Description |
|---|---|---|
| 1. netscape | netscape & | Run Netscape browser |
| 2. xv | xv & | Run graphics file converter |
| 3. xfig / xpaint | xfig & (xpaint &) | Run drawing program |
| 4. gimp | gimp & | Run photoshop type program |
| 5. ispell <fname> | ispell file1 | Spell check file1 |
| 6. latex <fname> | latex file.tex | Run LaTeX, a scientific document tool |
| 7. xemacs / pico | xemacs (or pico) | Different editors |
| 8. soffice | soffice & | Run StarOffice, a full word processor |
| 9. m-tools (mdir, mcopy, mdel, mformat, etc. ) | mdir a: mcopy file1 a: | DOS commands from UNIX (dir A:) Copy file1 to A: |
| 10. gnuplot | gnuplot | Plot data graphically |
Ten USEFUL UNIX Commands:
These ten commands are useful for monitoring system access, or simplifying your own environment.| Command | Example | Description |
|---|---|---|
| 1. df | df | See how much free disk space |
| 2. du | du -b subdir | Estimate disk usage of directory in Bytes |
| 3. alias | alias lls="ls -alF" | Create new command "lls" for long format of ls |
| 4. xhost | xhost + threat.tjhsst.edu xhost - | Permit window to display from x-window program from threat Allow no x-window access from other systems |
| 5. fold | fold -s file1 | lpr | Fold or break long lines at 60 characters and send to printer |
| 6. tar | tar -cf subdir.tar subdir tar -xvf subdir.tar | Create an archive called subdir.tar of a directory Extract files from an archive file |
| 7. ghostview (gv) | gv filename.ps | View a Postscript file |
| 8. ping (traceroute) | ping threat.tjhsst.edu traceroute www.yahoo.com | See if machine is alive Print data path to a machine |
| 9. top | top | Print system usage and top resource hogs |
| 10. logout (exit) | logout or exit | How to quit a UNIX shell. |
Helpful Files
The following files may be useful when trying to write your PVM programs in this class.- The online UNIX Dictionary of over 40,000 words:
/usr/dict/words The UNIX dictionary
- Some useful system files in the directory /etc or /usr/games/lib/fortune:
/etc/passwd The password file /etc/HOSTNAME The name of the computer /etc/issue The logon banner /usr/games/lib/fortunes/fortune The source for UNIX fortunes
Some Useful Commands
- Word Count, or "wc"
A helpful UNIX command is the "word count" program that can count how many words are in the file.
wc -w <filename> counts the number of words in a file
wc -l <filename> counts lines in a file.Grab Regular Expression, or "grep"
Another helpful command is "grep" for grabbing lines from a file that contain a specific string pattern, or regular expression. The command grep <string><files> looks through a list of files and finds lines that contain the specific word in the string argument.
grep pvm_pack *.cpp will look for occurrences of the string "pvm_pack" in all files ending in ".cpp".
grep "My name is" * will look in all files in a directory trying to find the string "My name is".Input / Output Redirection
The UNIX operating system has a number of useful tools for allowing other programs to work with one another. One of the ways to handle screen input and output with I/O Redirection, and ways to link several programs together with "pipes".With the use of the > for sending output to a file, a user can easily covert from screen display programs to ones that save the output without major changes in rewriting code. It is also very convenien for grabbing the output from various UNIX commands, too.- myprogram > myoutfile
This takes the output of "myprogram" and sends it a file called "myoutfile".ls -alF > filelist
This runs the command "ls", but saves the directory listing to a file rather than displaying it on the screen.
In order to convert a program that originally required lots of user input into one that runs on its own, the input redirection symbol < can be used to say where to get the values.
program2 < myinput
This runs "program2" but takes any keyboard input from the file "myinput". It is important the input values are in the proper sequence in the file "myinput" since there will not be ways to reply to prompts at the console.
Pipes
The vertical bar "|" is called the pipe symbol, and it is designed for linking commands together to make them more powerful. The way it works is that the output from one command is sent as input to the next, thus creating a new command.
ls -alF | grep ".cpp"
This will list all files in a directory, and will then grab the names of only the ones that contain the string ".cpp" in the name, or the C++ source files.
The system() command in C
The system() command is actually a C function that is very valuable for accessing UNIX commands from within a C program. It can also be used to run other programs you have already written. Be careful with extensive use of this command because according to the online manual pages (man), there are a few bugs such as not being able to break out of infinite loops because interrupts are not processed, and some other security issues. For many of the things we will be doing in this class, though, this command will be quite useful.- system( "ls - alF");
This will run the "ls" command from within a C program and display the results to the screen.
system ( "ps -aux | grep dhyatt > outfile");
This will run the "ps" command, the will send that output to "grep" which will look for occurrences of "dhyatt", and finally will print the results to a file called "outfile" rather than displaying anything on the screen. - About psReports the process status.ps [-a] [-A] [-c] [-d] [-e] [-f] [-j] [-l] [-L] [-P] [-y] [ -g grplist ] [ -n namelist ] [-o format ] [ -p proclist ] [ -s sidlist ] [ -t term] [ -u uidlist ] [ -U uidlist ] [ -G gidlist ]
-a List information about all processes most frequently requested: all those except process group leaders and processes not associated with a terminal. -A List information for all processes. Identical to -e, below. -c Print information in a format that reflects scheduler properties as described in priocntl.
The -c option affects the output of the -f and -l options, as described below.-d List information about all processes except session leaders. -e List information about every process now running. -f Generate a full listing. -j Print session ID and process group ID. -l Generate a long listing. -L Print information about each light weight process (lwp) in each selected process. -P Print the number of the processor to which the process or lwp is bound, if any, under an additional column header, PSR. -y Under a long listing (-l), omit the obsolete F and ADDR columns and include an RSS column to report the resident set size of the process. Under the -y option, both RSS and SZ will be reported in units of kilobytes instead of pages. -g grplist List only process data whose group leader's ID number(s) appears in grplist. (A group leader is a process whose process ID number is identical to its process group ID number.) -n namelist Specify the name of an alternative system namelist file in place of the default. This option is accepted for compatibility, but is ignored. -o format Print information according to the format specification given in format. This is fully described in DISPLAY FORMATS. Multiple -o options can be specified; the format specification will be interpreted as the space-character-separated concatenation of all the format option-arguments. -p proclist List only process data whose process ID numbers are given in proclist. -s sidlist List information on all session leaders whose IDs appear in sidlist. -t term List only process data associated with term. Terminal identifiers are specified as a device file name, and an identifier. For example, term/a, or pts/0. -u uidlist List only process data whose effective user ID number or login name is given in uidlist. In the listing, the numerical user ID will be printed unless you give the -f option, which prints the login name. -U uidlist List information for processes whose real user ID numbers or login names are given in uidlist. The uidlist must be a single argument in the form of a blank- or comma-separated list. -G gidlist List information for processes whose real group ID numbers are given in gidlist. The gidlist must be a single argument in the form of a blank- or comma-separated list. psTyping ps alone would list the current running processes. Below is an example of the output that would be generated by the ps command.PID TTY TIME CMD
6874 pts/9 0:00 ksh
6877 pts/9 0:01 csh
418 pts/9 0:00 cshps -efDisplay full information about each of the processes currently running.UID PID PPID C STIME TTY TIME CMD
hope 29197 18961 0 Sep27 ? 00:00:06 sshd: hope@pts/87
hope 32097 29197 0 Sep27 pts/87 00:00:00 -csh
hope 7209 32097 0 12:17 pts/87 00:00:00 ps -efps -lDisplays processes including those that are in a wait state, similar to the below example.F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD 0 T 0 12308 29722 0 80 0 - 16136 finish pts/0 00:00:00 pico 0 R 0 12530 29722 0 80 0 - 15884 - pts/0 00:00:00 ps 4 S 0 29722 29581 0 80 0 - 16525 wait pts/0 00:00:00 bash. 20 Linux System Monitoring Tools Every SysAdmin Should Know
Need to monitor Linux server performance? Try these built-in command and a few add-on tools. Most Linux distributions are equipped with tons of monitoring. These tools provide metrics which can be used to get information about system activities. You can use these tools to find the possible causes of a performance problem. The commands discussed below are some of the most basic commands when it comes to system analysis and debugging server issues such as:- Finding out bottlenecks.
- Disk (storage) bottlenecks.
- CPU and memory bottlenecks.
- Network bottlenecks.
#1: top - Process Activity Command
The top program provides a dynamic real-time view of a running system i.e. actual process activity. By default, it displays the most CPU-intensive tasks running on the server and updates the list every five seconds.
Fig.01: Linux top commandCommonly Used Hot Keys
The top command provides several useful hot keys:Hot Key Usage t Displays summary information off and on. m Displays memory information off and on. A Sorts the display by top consumers of various system resources. Useful for quick identification of performance-hungry tasks on a system. f Enters an interactive configuration screen for top. Helpful for setting up top for a specific task. o Enables you to interactively select the ordering within top. r Issues renice command. k Issues kill command. z Turn on or off color/mono
=> Related: How do I Find Out Linux CPU Utilization?#2: vmstat - System Activity, Hardware and System Information
The command vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity.# vmstat 3
Sample Outputs:procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 0 0 0 2540988 522188 5130400 0 0 2 32 4 2 4 1 96 0 0 1 0 0 2540988 522188 5130400 0 0 0 720 1199 665 1 0 99 0 0 0 0 0 2540956 522188 5130400 0 0 0 0 1151 1569 4 1 95 0 0 0 0 0 2540956 522188 5130500 0 0 0 6 1117 439 1 0 99 0 0 0 0 0 2540940 522188 5130512 0 0 0 536 1189 932 1 0 98 0 0 0 0 0 2538444 522188 5130588 0 0 0 0 1187 1417 4 1 96 0 0 0 0 0 2490060 522188 5130640 0 0 0 18 1253 1123 5 1 94 0 0Display Memory Utilization Slabinfo
# vmstat -mGet Information About Active / Inactive Memory Pages
# vmstat -a
=> Related: How do I find out Linux Resource utilization to detect system bottlenecks?#3: w - Find Out Who Is Logged on And What They Are Doing
w command displays information about the users currently on the machine, and their processes.# w username
# w vivek
Sample Outputs:17:58:47 up 5 days, 20:28, 2 users, load average: 0.36, 0.26, 0.24 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT root pts/0 10.1.3.145 14:55 5.00s 0.04s 0.02s vim /etc/resolv.conf root pts/1 10.1.3.145 17:43 0.00s 0.03s 0.00s w#4: uptime - Tell How Long The System Has Been Running
The uptime command can be used to see how long the server has been running. The current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.# uptime
Output:18:02:41 up 41 days, 23:42, 1 user, load average: 0.00, 0.00, 0.001 can be considered as optimal load value. The load can change from system to system. For a single CPU system 1 - 3 and SMP systems 6-10 load value might be acceptable.#5: ps - Displays The Processes
ps command will report a snapshot of the current processes. To select all processes use the -A or -e option:# ps -A
Sample Outputs:PID TTY TIME CMD 1 ? 00:00:02 init 2 ? 00:00:02 migration/0 3 ? 00:00:01 ksoftirqd/0 4 ? 00:00:00 watchdog/0 5 ? 00:00:00 migration/1 6 ? 00:00:15 ksoftirqd/1 .... ..... 4881 ? 00:53:28 java 4885 tty1 00:00:00 mingetty 4886 tty2 00:00:00 mingetty 4887 tty3 00:00:00 mingetty 4888 tty4 00:00:00 mingetty 4891 tty5 00:00:00 mingetty 4892 tty6 00:00:00 mingetty 4893 ttyS1 00:00:00 agetty 12853 ? 00:00:00 cifsoplockd 12854 ? 00:00:00 cifsdnotifyd 14231 ? 00:10:34 lighttpd 14232 ? 00:00:00 php-cgi 54981 pts/0 00:00:00 vim 55465 ? 00:00:00 php-cgi 55546 ? 00:00:00 bind9-snmp-stat 55704 pts/1 00:00:00 psps is just like top but provides more information.Show Long Format Output
# ps -Al
To turn on extra full mode (it will show command line arguments passed to process):# ps -AlFTo See Threads ( LWP and NLWP)
# ps -AlFHTo See Threads After Processes
# ps -AlLmPrint All Process On The Server
# ps ax
# ps axuPrint A Process Tree
# ps -ejH
# ps axjf
# pstreePrint Security Information
# ps -eo euser,ruser,suser,fuser,f,comm,label
# ps axZ
# ps -eMSee Every Process Running As User Vivek
# ps -U vivek -u vivek uSet Output In a User-Defined Format
# ps -eo pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:14,comm
# ps axo stat,euid,ruid,tty,tpgid,sess,pgrp,ppid,pid,pcpu,comm
# ps -eopid,tt,user,fname,tmout,f,wchanDisplay Only The Process IDs of Lighttpd
# ps -C lighttpd -o pid=
OR# pgrep lighttpd
OR# pgrep -u vivek php-cgiDisplay The Name of PID 55977
# ps -p 55977 -o comm=Find Out The Top 10 Memory Consuming Process
# ps -auxf | sort -nr -k 4 | head -10Find Out top 10 CPU Consuming Process
# ps -auxf | sort -nr -k 3 | head -10#6: free - Memory Usage
The command free displays the total amount of free and used physical and swap memory in the system, as well as the buffers used by the kernel.# free
Sample Output:total used free shared buffers cached Mem: 12302896 9739664 2563232 0 523124 5154740 -/+ buffers/cache: 4061800 8241096 Swap: 1052248 0 1052248#7: iostat - Average CPU Load, Disk Activity
The command iostat report Central Processing Unit (CPU) statistics and input/output statistics for devices, partitions and network filesystems (NFS).# iostat
Sample Outputs:Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in) 06/26/2009 avg-cpu: %user %nice %system %iowait %steal %idle 3.50 0.09 0.51 0.03 0.00 95.86 Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn sda 22.04 31.88 512.03 16193351 260102868 sda1 0.00 0.00 0.00 2166 180 sda2 22.04 31.87 512.03 16189010 260102688 sda3 0.00 0.00 0.00 1615 0=> Related: : Linux Track NFS Directory / Disk I/O Stats#8: sar - Collect and Report System Activity
The sar command is used to collect, report, and save system activity information. To see network counter, enter:# sar -n DEV | more
To display the network counters from the 24th:# sar -n DEV -f /var/log/sa/sa24 | more
You can also display real time usage using sar:# sar 4 5
Sample Outputs:Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in) 06/26/2009 06:45:12 PM CPU %user %nice %system %iowait %steal %idle 06:45:16 PM all 2.00 0.00 0.22 0.00 0.00 97.78 06:45:20 PM all 2.07 0.00 0.38 0.03 0.00 97.52 06:45:24 PM all 0.94 0.00 0.28 0.00 0.00 98.78 06:45:28 PM all 1.56 0.00 0.22 0.00 0.00 98.22 06:45:32 PM all 3.53 0.00 0.25 0.03 0.00 96.19 Average: all 2.02 0.00 0.27 0.01 0.00 97.70#9: mpstat - Multiprocessor Usage
The mpstat command displays activities for each available processor, processor 0 being the first one. mpstat -P ALL to display average CPU utilization per processor:# mpstat -P ALL
Sample Output:Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in) 06/26/2009 06:48:11 PM CPU %user %nice %sys %iowait %irq %soft %steal %idle intr/s 06:48:11 PM all 3.50 0.09 0.34 0.03 0.01 0.17 0.00 95.86 1218.04 06:48:11 PM 0 3.44 0.08 0.31 0.02 0.00 0.12 0.00 96.04 1000.31 06:48:11 PM 1 3.10 0.08 0.32 0.09 0.02 0.11 0.00 96.28 34.93 06:48:11 PM 2 4.16 0.11 0.36 0.02 0.00 0.11 0.00 95.25 0.00 06:48:11 PM 3 3.77 0.11 0.38 0.03 0.01 0.24 0.00 95.46 44.80 06:48:11 PM 4 2.96 0.07 0.29 0.04 0.02 0.10 0.00 96.52 25.91 06:48:11 PM 5 3.26 0.08 0.28 0.03 0.01 0.10 0.00 96.23 14.98 06:48:11 PM 6 4.00 0.10 0.34 0.01 0.00 0.13 0.00 95.42 3.75 06:48:11 PM 7 3.30 0.11 0.39 0.03 0.01 0.46 0.00 95.69 76.89#10: pmap - Process Memory Usage
The command pmap report memory map of a process. Use this command to find out causes of memory bottlenecks.# pmap -d PID
To display process memory information for pid # 47394, enter:# pmap -d 47394
Sample Outputs:47394: /usr/bin/php-cgi Address Kbytes Mode Offset Device Mapping 0000000000400000 2584 r-x-- 0000000000000000 008:00002 php-cgi 0000000000886000 140 rw--- 0000000000286000 008:00002 php-cgi 00000000008a9000 52 rw--- 00000000008a9000 000:00000 [ anon ] 0000000000aa8000 76 rw--- 00000000002a8000 008:00002 php-cgi 000000000f678000 1980 rw--- 000000000f678000 000:00000 [ anon ] 000000314a600000 112 r-x-- 0000000000000000 008:00002 ld-2.5.so 000000314a81b000 4 r---- 000000000001b000 008:00002 ld-2.5.so 000000314a81c000 4 rw--- 000000000001c000 008:00002 ld-2.5.so 000000314aa00000 1328 r-x-- 0000000000000000 008:00002 libc-2.5.so 000000314ab4c000 2048 ----- 000000000014c000 008:00002 libc-2.5.so ..... ...... .. 00002af8d48fd000 4 rw--- 0000000000006000 008:00002 xsl.so 00002af8d490c000 40 r-x-- 0000000000000000 008:00002 libnss_files-2.5.so 00002af8d4916000 2044 ----- 000000000000a000 008:00002 libnss_files-2.5.so 00002af8d4b15000 4 r---- 0000000000009000 008:00002 libnss_files-2.5.so 00002af8d4b16000 4 rw--- 000000000000a000 008:00002 libnss_files-2.5.so 00002af8d4b17000 768000 rw-s- 0000000000000000 000:00009 zero (deleted) 00007fffc95fe000 84 rw--- 00007ffffffea000 000:00000 [ stack ] ffffffffff600000 8192 ----- 0000000000000000 000:00000 [ anon ] mapped: 933712K writeable/private: 4304K shared: 768000KThe last line is very important:- mapped: 933712K total amount of memory mapped to files
- writeable/private: 4304K the amount of private address space
- shared: 768000K the amount of address space this process is sharing with others
#11 and #12: netstat and ss - Network Statistics
The command netstat displays network connections, routing tables, interface statistics, masquerade connections, and multicast memberships. ss command is used to dump socket statistics. It allows showing information similar to netstat. See the following resources about ss and netstat commands:- ss: Display Linux TCP / UDP Network and Socket Information
- Get Detailed Information About Particular IP address Connections Using netstat Command
#13: iptraf - Real-time Network Statistics
The iptraf command is interactive colorful IP LAN monitor. It is an ncurses-based IP LAN monitor that generates various network statistics including TCP info, UDP counts, ICMP and OSPF information, Ethernet load info, node stats, IP checksum errors, and others. It can provide the following info in easy to read format:- Network traffic statistics by TCP connection
- IP traffic statistics by network interface
- Network traffic statistics by protocol
- Network traffic statistics by TCP/UDP port and by packet size
- Network traffic statistics by Layer2 address
Fig.02: General interface statistics: IP traffic statistics by network interface
Fig.03 Network traffic statistics by TCP connection#14: tcpdump - Detailed Network Traffic Analysis
The tcpdump is simple command that dump traffic on a network. However, you need good understanding of TCP/IP protocol to utilize this tool. For.e.g to display traffic info about DNS, enter:# tcpdump -i eth1 'udp port 53'
To display all IPv4 HTTP packets to and from port 80, i.e. print only packets that contain data, not, for example, SYN and FIN packets and ACK-only packets, enter:# tcpdump 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
To display all FTP session to 202.54.1.5, enter:# tcpdump -i eth1 'dst 202.54.1.5 and (port 21 or 20'
To display all HTTP session to 192.168.1.5:# tcpdump -ni eth0 'dst 192.168.1.5 and tcp and port http'
Use wireshark to view detailed information about files, enter:# tcpdump -n -i eth1 -s 0 -w output.txt src or dst port 80#15: strace - System Calls
Trace system calls and signals. This is useful for debugging webserver and other server problems. See how to use to trace the process and see What it is doing.#16: /Proc file system - Various Kernel Statistics
/proc file system provides detailed information about various hardware devices and other Linux kernel information. See Linux kernel /proc documentations for further details. Common /proc examples:# cat /proc/cpuinfo
# cat /proc/meminfo
# cat /proc/zoneinfo
# cat /proc/mounts17#: Nagios - Server And Network Monitoring
Nagios is a popular open source computer system and network monitoring application software. You can easily monitor all your hosts, network equipment and services. It can send alert when things go wrong and again when they get better. FAN is "Fully Automated Nagios". FAN goals are to provide a Nagios installation including most tools provided by the Nagios Community. FAN provides a CDRom image in the standard ISO format, making it easy to easilly install a Nagios server. Added to this, a wide bunch of tools are including to the distribution, in order to improve the user experience around Nagios.18#: Cacti - Web-based Monitoring Tool
Cacti is a complete network graphing solution designed to harness the power of RRDTool's data storage and graphing functionality. Cacti provides a fast poller, advanced graph templating, multiple data acquisition methods, and user management features out of the box. All of this is wrapped in an intuitive, easy to use interface that makes sense for LAN-sized installations up to complex networks with hundreds of devices. It can provide data about network, CPU, memory, logged in users, Apache, DNS servers and much more. See how to install and configure Cacti network graphing tool under CentOS / RHEL.#19: KDE System Guard - Real-time Systems Reporting and Graphing
KSysguard is a network enabled task and system monitor application for KDE desktop. This tool can be run over ssh session. It provides lots of features such as a client/server architecture that enables monitoring of local and remote hosts. The graphical front end uses so-called sensors to retrieve the information it displays. A sensor can return simple values or more complex information like tables. For each type of information, one or more displays are provided. Displays are organized in worksheets that can be saved and loaded independently from each other. So, KSysguard is not only a simple task manager but also a very powerful tool to control large server farms.
Fig.05 KDE System Guard {Image credit: Wikipedia}See the KSysguard handbook for detailed usage.#20: Gnome System Monitor - Real-time Systems Reporting and Graphing
The System Monitor application enables you to display basic system information and monitor system processes, usage of system resources, and file systems. You can also use System Monitor to modify the behavior of your system. Although not as powerful as the KDE System Guard, it provides the basic information which may be useful for new users:- Displays various basic information about the computer's hardware and software.
- Linux Kernel version
- GNOME version
- Hardware
- Installed memory
- Processors and speeds
- System Status
- Currently available disk space
- Processes
- Memory and swap space
- Network usage
- File Systems
- Lists all mounted filesystems along with basic information about each.
Fig.06 The Gnome System Monitor applicationBonus: Additional Tools
A few more tools:- nmap - scan your server for open ports.
- lsof - list open files, network connections and much more.
- ntop web based tool - ntop is the best tool to see network usage in a way similar to what top command does for processes i.e. it is network traffic monitoring software. You can see network status, protocol wise distribution of traffic for UDP, TCP, DNS, HTTP and other protocols.
- Conky - Another good monitoring tool for the X Window System. It is highly configurable and is able to monitor many system variables including the status of the CPU, memory, swap space, disk storage, temperatures, processes, network interfaces, battery power, system messages, e-mail inboxes etc.
- GKrellM - It can be used to monitor the status of CPUs, main memory, hard disks, network interfaces, local and remote mailboxes, and many other things.
- vnstat - vnStat is a console-based network traffic monitor. It keeps a log of hourly, daily and monthly network traffic for the selected interface(s).
- htop - htop is an enhanced version of top, the interactive process viewer, which can display the list of processes in a tree form.
- mtr - mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.
Did I miss something? Please add your favorite system motoring tool in the comments.
- For More Commands Follow Below Links
- http://linux.about.com/od/commands
- http://www.computerhope.com/unix
- http://www.cyberciti.biz
- myprogram > myoutfile
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