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Linux — Network Communication Utilities

Short & clear revision notes · 4 topics

01 · ping — Check if a Host is Reachable

The ping command sends an echo request to a host on the network and waits for a reply. Used to test whether a remote machine is alive and responding.

ping hostname
ping ip-address

Press Ctrl+C to stop — it runs continuously until interrupted.

What ping is useful for

  • Checking if a remote host is up or down
  • Tracking and isolating network/hardware problems
  • Testing network speed and measuring latency

Example

$ ping google.com
PING google.com (74.125.67.100) 56(84) bytes of data.
64 bytes from 74.125.67.100: icmp_seq=1 ttl=54 time=39.4 ms
64 bytes from 74.125.67.100: icmp_seq=2 ttl=54 time=39.9 ms
--- google.com ping statistics ---
22 packets transmitted, 22 received, 0% packet loss

Reading the output

Field Meaning
icmp_seq Packet sequence number
ttl Time To Live — hops remaining before packet is dropped
time Round-trip time in milliseconds (lower = faster)
packet loss % of packets that never came back (0% = healthy)

If the host doesn't exist

$ ping giiiiiigle.com
ping: unknown host giiiiigle.com

02 · ftp — Transfer Files Between Machines

ftp (File Transfer Protocol) lets you upload and download files between a local and a remote machine.

ftp hostname
ftp ip-address

After connecting, you enter your login ID and password, then use ftp's own set of commands inside the ftp shell.

ftp commands

Command What it does
put filename Upload one file from local → remote
get filename Download one file from remote → local
mput file list Upload multiple files at once
mget file list Download multiple files at once
prompt off Turn off per-file confirmation for mput/mget
prompt on Turn confirmation back on
dir List files in the current directory on the remote machine
cd dirname Change directory on the remote machine
lcd dirname Change directory on the local machine
quit Log out and close the ftp connection

Example session

$ ftp amrood.com
Name: amrood
Password: ****
230 User amrood logged in.

ftp> dir               # list remote files
ftp> cd mpl            # navigate remote directory
ftp> get wave_shift    # download a file
528454 bytes received in 1.296 seconds (398.1 Kbytes/s)
ftp> quit
221 Goodbye.

💡 Files are always downloaded/uploaded to your current local directory. Use lcd to change it before transferring files.

03 · telnet — Log Into a Remote Machine

telnet lets you connect to a remote Unix machine over the network and work on it as if you were sitting at it.

telnet hostname

After connecting you get a login prompt, enter credentials, and then work in the remote shell normally. Type logout to disconnect.

Example session

$ telnet amrood.com
Trying...
Connected to amrood.com.
login: amrood
Password: ****
{ do your work }
$ logout
Connection closed.

⚠️ Telnet sends data including passwords in plain text — it is not secure. In modern systems, SSH is used instead of telnet for remote login.

04 · finger — Look Up User Information

The finger command displays information about users on a local or remote host — their login name, home directory, shell, login time, and more.

finger                       # all logged-in users on local machine
finger username              # specific user on local machine
finger @hostname             # all logged-in users on remote machine
finger username@hostname     # specific user on remote machine

Examples

# All users logged into local machine
$ finger
Login    Name   Tty   Idle  Login Time
amrood          pts/0       Jun 25 08:03 (62.61.164.115)

# Detailed info for a specific user
$ finger amrood
Login: amrood          Directory: /home/amrood
Shell: /bin/bash
On since Thu Jun 25 08:03 on pts/0 from 62.61.164.115
No mail.

# Users on a remote machine
$ finger @avtar.com

# Specific user on remote machine
$ finger amrood@avtar.com

⚠️ finger is often disabled on remote systems for security reasons — it can expose user information to outsiders.

Quick Reference

ping:
  ping google.com            # check if host is reachable
  ping 192.168.1.1           # ping by IP address
  Ctrl+C                     # stop pinging

ftp:
  ftp hostname               # connect to remote machine
  get filename               # download a file
  put filename               # upload a file
  mget *.txt                 # download multiple files
  lcd /local/dir             # change local directory first
  dir                        # list remote directory
  quit                       # disconnect

telnet:
  telnet hostname            # remote login (use SSH in practice)
  logout                     # disconnect

finger:
  finger                     # local users
  finger username            # specific local user
  finger @hostname           # remote users
  finger user@hostname       # specific remote user

Linux Network Communication Utilities Notes — for revision use