The network commands chapter explains various tools which can be useful when networking with other computers both within the network and accross the internet, obtaining more information about other computers. This chapter also includes information on tools for network configuration, file transfer and working with remote machines.
- Displays contents of /proc/net files. It works with the Linux Network Subsystem, it will tell you what the status of ports are ie. open, closed, waiting, masquerade connections. It will also display various other things. It has many different options.
- This is a sniffer, a program that captures packets off a network interface and interprets them for you. It understands all basic internet protocols, and can be used to save entire packets for later inspection.
- The ping command (named after the sound of an active sonar system) sends echo requests to the host you specify on the command line, and lists the responses received their round trip time.You simply use ping as:
Please note: Using ping/smbmount/ssh or other UNIX system programs with a computer name rather than IP address will only work if you have the computer listed in your /etc/hosts file. Here is an example:
- Tells the user the host name of the computer they are logged into. Note: may be called host.
- traceroute will show the route of a packet. It attempts to list the series of hosts through which your packets travel on their way to a given destination. Also have a look at xtraceroute (one of several graphical equivalents of this program).Command syntax:
- tracepath performs a very simlar function to traceroute the main difference is that tracepath doesn’t take complicated options.Command syntax:
- findsmb is used to list info about machines that respond to SMB name queries (for example windows based machines sharing their hard disk’s).Command syntax:
- “ network exploration tool and security scanner”. nmap is a very advanced network tool used to query machines (local or remote) as to whether they are up and what ports are open on these machines.A simple usage example:
This would query your own machine as to what ports it keeps open. nmap is a very powerful tool, documentation is available on the nmap site as well as the information in the manual page.
- This command is used to configure network interfaces, or to display their current configuration. In addition to activating and deactivating interfaces with the “up” and “down” settings, this command is necessary for setting an interface’s address information if you don’t have the ifcfg script.Use ifconfig as either:
ifconfig eth0 down
- Use ifup device-name to bring an interface up by following a script (which will contain your default networking settings). Simply type ifup and you will get help on using the script.For example typing:
- Use ifdown device-name to bring an interface down using a script (which will contain your default network settings). Simply type ifdown and you will get help on using the script.For example typing:
- Use ifcfg to configure a particular interface. Simply type ifcfg to get help on using this script.For example, to change eth0 from 192.168.0.1 to 192.168.0.2 you could do:
ifcfg eth0 del 192.168.0.1 ifcfg eth0 add 192.168.0.2
- The route command is the tool used to display or modify the routing table. To add a gateway as the default you would type:
route add default gw some_computer
Internet Specific Commands
- Performs a simple lookup of an internet address (using the Domain Name System, DNS). Simply type:
- The “domain information groper” tool. More advanced then host… If you give a hostname as an argument to output information about that host, including it’s IP address, hostname and various other information.For example, to look up information about “www.amazon.com” type:
dig -x 22.214.171.124
This will look up the address (which may or may not exist) and returns the address of the host, for example if that was the address of “http://slashdot.org” then it would return “http://slashdot.org”.
- (now BW whois) is used to look up the contact information from the “whois” databases, the servers are only likely to hold major sites. Note that contact information is likely to be hidden or restricted as it is often abused by crackers and others looking for a way to cause malicious damage to organisation’s.
- (GNU Web get) used to download files from the World Wide Web.To archive a single web-site, use the -m or –mirror (mirror) option.Use the -nc (no clobber) option to stop wget from overwriting a file if you already have it.
wget can also retrieve multiple files using standard wildcards, the same as the type used in bash, like *, [ ], ?. Simply use wget as per normal but use single quotation marks (‘ ‘) on the URL to prevent bash from expanding the wildcards. There are complications if you are retrieving from a http site (see below…).
wget --spider --force-html -i bookmarks.html
wget -r -l1 --no-parent -A.gif http://www.website.com
This will download (recursively), to a depth of one, in other words in the current directory and not below that. This command will ignore references to the parent directory, and downloads anything that ends in “.gif”. If you wanted to download say, anything that ends with “.pdf” as well than add a -A.pdf before the website address. Simply change the website address and the type of file being downloaded to download something else. Note that doing -A.gif is the same as doing -A “*.gif” (double quotes only, single quotes will not work).
- curl is another remote downloader. This remote downloader is designed to work without user interaction and supports a variety of protocols, can upload/download and has a large number of tricks/work-arounds for various things. It can access dictionary servers (dict), ldap servers, ftp, http, gopher, see the manual page for full details.To access the full manual (which is huge) for this command type:
curl -u usernameassword http://www.placetodownload/file
curl -T file_name ftp://ftp.uploadsite.com
curl -C - -o file http://www.site.com
Remote Administration Related
Secure shell, remotely login on a machine running the sshd daemon. Once you are logged in you have a secure shell and are able to execute various commands on that computer such as copy files, reboot the computer, just like it was your own GNU/Linux PC.
Or you can use ssh with a full hostname to connect to a remote machine (as in across the internet).
Connect to a remote system with your current username, you will obviously need the password of the user on the other machine.
Connect to a remote system with your a different username, you will obviously need the password of the user on the other machine.
Secure copy, part of the ssh package. Allows you to copy files from one computer to another computer, use -r to copy recursively (copy entire directories and subdirectories).
scp’s syntax is always
scp machineToBeCopiedFrom machineToBeCopiedTo
Where either machine can be a local directory (on the current filesystem /) or a remote machine. Remote machines are usually machinesFullName:/directory (if you omit the directory part it will just assume the home directory of the username you are logging in with).
The example below copies all files from the current directory (not including any directories), the command will login to “new” using the username of the person currently logged in on the local computer, the files will be copied to the root directory of the remote computer called “new” (which is probably on the LAN):
scp * new:/
You could also copy files from another computer to another computer. Let’s say you are on a computer called “p100”. And you want to copy files (and directories) from “hp166” (in the /tmp directory and anything below that) to “new” and put the files in new’s temporary directory. You could do:
scp -r hp166:/tmp new:/tmp
Assuming you were logged in as “fred” you would need passwords for user “fred” on the computers hp166 and new. Add an user_name@ before the computer name to login under a different user name.
For example to perform the above command with user “root” on hp166 and “anon” on new you would type:
scp -r root@hp166:/tmp anon@new:/tmp
To copy from a remote machine to a local computer you simply do things in reverse:
scp remoteMachine:/mystuff/* .
This will copy files on the remote machine in the directory “mystuff” to your local computer.
Remote Machines: Please note that when working with a remote machine you need to have a : (colon) after the machine name even if you want the files in their home directory. Otherwise the command will fail.
Secure ftp, another part of the ssh package. This command is similar to ftp but uses an encrypted tunnel to connect to an ftp server and is therefore more secure than just plain ftp.
The command usage is very similar to ftp (the command-line tool), sftp (once running) uses commands such as help (for help), put (send files to the server), get (download files from the server) and various others, refer to the manual page and internal documentation for further details.