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Linux Commands — System Information
command code Notes
arch Display the processor architecture of the machine (1)
uname -m Display the processor architecture of the machine (2)
uname -r Display the kernel version in use
dmidecode -q Display Hardware System Components - (SMBIOS / DMI)
hdparm -i /dev/hda List the architectural properties of a disk
hdparm -tT /dev/sda Perform a test read on disk
cat /proc/cpuinfo Display CPU info information
cat /proc/interrupts Display Interrupt
cat /proc/meminfo Check memory usage
cat /proc/swaps Show which swap is used
cat /proc/version Show kernel version
cat /proc/net/dev Show network adapters and statistics
cat /proc/mounts Show mounted filesystems
lspci -tv List PCI devices
lsusb -tv Show usb devices
date Display system date
cal 2007 Display the calendar for 2007
date 041217002007.00 Set date and time - month day hour minute year.second
clock -w Save time changes to BIOS
Linux Commands — System Shutdown (Shutdown, Restart, and Logout)
command code Notes
shutdown -h now Shut down the system
init 0 Shut down the system
telinit 0 Shut down the system
shutdown -h hours:minutes & Shut down the system at a scheduled time
shutdown -c Cancel shutting down the system at a scheduled time
shutdown -r now Restart
reboot Restart
logout Logout
Linux Commands — Files and Directories
command code Notes
cd /home Enter the '/home' directory'
cd .. Back to the previous directory
cd ../.. Back to the previous two levels of directory
cd Enter your home directory
cd ~user1 Enter your home directory
cd - Return to last directory
pwd Show working path
ls View files in directory
ls -F View files in directory
ls -l Display file and directory details
ls -a Show hidden files
ls *[0-9]* Display file and directory names containing numbers
tree Display the tree structure of files and directories starting from the root directory
lstree Display the tree structure of files and directories starting from the root directory
mkdir dir1 Create a directory called 'dir1'
mkdir dir1 dir2 Create two directories at the same time
mkdir -p /tmp/dir1/dir2 Create a directory tree
rm -f file1 Deleting a file called 'file1''
rmdir dir1 Delete a directory called 'dir1'
rm -rf dir1 Delete a directory called 'dir1' and its contents
rm -rf dir1 dir2 Delete both directories and their contents at the same time
mv dir1 new_dir Rename/move a directory
cp file1 file2 Copy a file
cp dir/* . Copy all files in a directory to the current working directory
cp -a /tmp/dir1 . Copy a directory to the current working directory
cp -a dir1 dir2 Copy a directory
ln -s file1 lnk1 Create a soft link to a file or directory
ln file1 lnk1 Create a physical link to a file or directory
touch -t 0712250000 file1 Modify a file or directory timestamp - (YYMMDDhhmm)
iconv -l List known encodings
iconv -f fromEncoding -t toEncoding inputFile > outputFile Change character encoding
find . -maxdepth 1 -name *.jpg -print -exec convert Batch resize files in the current directory and send them to the thumbnail directory (requires conversion from ImageMagick)
Linux Commands — File Search
command code Notes
find / -name file1 Start from '/' to enter the root file system to search for files and directories
find / -user user1 Search for files and directories belonging to user 'user1'
find /home/user1 -name \*.bin Search for files ending with '.bin' in directory '/home/user1'
find /usr/bin -type f -atime +100 Search for executable files that have not been used in the past 100 days
find /usr/bin -type f -mtime -10 Search for files that were created or modified within 10 days
find / -name \*.rpm -exec chmod 755 '{}' \; Search for files ending in '.rpm' and define their permissions
find / -xdev -name \*.rpm Search for files ending with '.rpm', ignoring removable devices such as CD-ROMs and shortcuts
locate \*.ps Look for files ending in '.ps' - run 'updatedb' first
where is halt Display the location of a binary, source or man
which halt Display the full path to a binary or executable
Linux command — mount a filesystem
command code Notes
mount /dev/hda2 /mnt/hda2 Mount a disk called hda2 - make sure the directory '/mnt/hda2' already exists
umount /dev/hda2 Unmount a disk called hda2 - first exit from the mount point '/mnt/hda2'
fuser -km /mnt/hda2 Force unmount when device is busy
umount -n /mnt/hda2 Run the unmount without writing to the /etc/mtab file - useful when the file is read-only or when the disk is full
mount /dev/fd0 /mnt/floppy Mount a floppy
mount /dev/cdrom /mnt/cdrom Mount a cdrom or dvdrom
mount /dev/hdc /mnt/cdrecorder Mount a cdrw or dvdrom
mount /dev/hdb /mnt/cdrecorder Mount a cdrw or dvdrom
mount -o loop file.iso /mnt/cdrom Mount a file or ISO image
mount -t vfat /dev/hda5 /mnt/hda5 Mount a Windows FAT32 filesystem
mount /dev/sda1 /mnt/usbdisk Mount a usb stick or flash drive
mount -t smbfs -o username=user,password=pass //WinClient/share /mnt/share Mount a windows network share
Linux Commands — Disk Space
command code Notes
df -h Display the list of mounted partitions
ls -lSr |more Arrange files and directories by size
du -sh dir1 Estimated disk space used by directory 'dir1''
du -sk * | sort -rn Display the size of files and directories in sequence based on the size of the capacity
rpm -q -a --qf '%10{SIZE}t%{NAME}n' | sort -k1,1n Display the space used by the installed rpm packages according to the size (fedora, redhat-like systems)
dpkg-query -W -f='${Installed-Size;10}t${Package}n' | sort -k1,1n Display the space used by installed deb packages by size (ubuntu, debian-like systems)
Linux Commands — Users and Groups
command code Notes
groupadd group_name Create a new user group
groupdel group_name Delete a user group
groupmod -n new_group_name old_group_name Rename a usergroup
useradd -c "Name Surname " -g admin -d /home/user1 -s /bin/bash user1 Create a user belonging to the "admin" usergroup
useradd user1 Create a new user
userdel -r user1 Remove a user ('-r' exclude home directory)
usermod -c "User FTP" -g system -d /ftp/user1 -s /bin/nologin user1 Modify user attributes
passwd Change password
passwd user1 Change a user's password (only root execution is allowed)
chage -E 2020-12-31 user1 Set user password expiration date
pwck Check '/etc/passwd' for file format and syntax corrections and existing users
grpck Check '/etc/passwd' for file format and syntax corrections and existing groups
newgrp group_name Log in to a new group to change the default group for newly created files
Linux command - file permissions - use "+" to set permissions, use "-" to cancel
command code Notes
ls -lh Show Permissions
ls /tmp | pr -T5 -W$COLUMNS Divide the terminal into 5 columns for display
chmod ugo+rwx directory1 Set the owner (u), group (g) and others (o) permissions of the directory to read (r), write (w) and execute (x) permissions
chmod go-rwx directory1 Delete group (g) and others (o) permissions to read, write, and execute directories
chown user1 file1 Change the owner attribute of a file
chown -R user1 directory1 Change the owner attribute of a directory and change the attributes of all files in the directory at the same time
chgrp group1 file1 Change the group of the file
chown user1:group1 file1 Change the owner and group attributes of a file
find / -perm -u+s List all files controlled by SUID in a system
chmod u+s /bin/file1 Set the SUID bit of a binary - the user who runs the file is given the same permissions as the owner
chmod u-s /bin/file1 Disable the SUID bit for a binary
chmod g+s /home/public Set the SGID bit of a directory - like SUID, but for directories
chmod g-s /home/public Disable the SGID bit for a directory
chmod o+t /home/public Set the STIKY bit on a file - only allow the rightful owner to delete the file
chmod o -t /home/public Disable the STIKY bit for a directory
Linux commands—special properties of files—use "+" to set permissions, use "- " for cancel
command code Notes
chattr +a file1 Only allow reading and writing files in append mode
chattr +c file1 Allow this file to be automatically compressed/decompressed by the kernel
chattr +d file1 The dump program will ignore this file when doing a file system backup
chattr +i file1 Set as an immutable file and cannot be deleted, modified, renamed or linked
chattr +s file1 Allows a file to be safely deleted
chattr +S file1 Once the application program writes to this file, the system immediately writes the modified results to disk
chattr +u file1 If the file is deleted, the system will allow you to restore the deleted file in the future
lsattr Display special attributes
Linux Commands — Pack and Compress Files
command code Notes
bunzip2 file1.bz2 Unzip a file called 'file1.bz2'
bzip2 file1 Compress a file called 'file1'
gunzip file1.gz Decompress a file called 'file1.gz'
gzip file1 Compress a file called 'file1'
gzip -9 file1 Maximum compression
rar a file1.rar test_file Create a package called 'file1.rar'
rar a file1.rar file1 file2 dir1 Compress 'file1', 'file2' and directory 'dir1' at the same time
rar x file1.rar Decompress the rar package
unrar x file1.rar Decompress the rar package
tar -cvf archive.tar file1 Create an uncompressed tarball
tar -cvf archive.tar file1 file2 dir1 Create an archive containing 'file1', 'file2' and 'dir1'
tar -tf archive.tar Display the contents of a package
tar -xvf archive.tar Release a package
tar -xvf archive.tar -C /tmp Release the compressed package to the /tmp directory
tar -cvfj archive.tar.bz2 dir1 Create a compressed package in bzip2 format
tar -jxvf archive.tar.bz2 Decompress a compressed package in bzip2 format
tar -cvfz archive.tar.gz dir1 Create a compressed package in gzip format
tar -zxvf archive.tar.gz Decompress a compressed package in gzip format
zip file1.zip file1 Create a compressed package in zip format
zip -r file1.zip file1 file2 dir1 Compress several files and directories into a compressed package in zip format
unzip file1.zip Decompress a zip file
Linux Commands - RPM Packages - (Fedora, Redhat and Similar)
command code Notes
rpm -ivh package.rpm Install an rpm package
rpm -ivh --nodeeps package.rpm Install an rpm package ignoring dependency warnings
rpm -U package.rpm Update an rpm package without changing its configuration file
rpm -F package.rpm Update a confirmed installed rpm package
rpm -e package_name.rpm Delete an rpm package
rpm -qa Display all installed rpm packages in the system
rpm -qa | grep httpd Show all rpm packages with "httpd" in their name
rpm -qi package_name Get special information about an installed package
rpm -qg "System Environment/Daemons" Display the rpm package of a component
rpm -ql package_name Display a list of files provided by an installed rpm package
rpm -qc package_name Display a list of configuration files provided by an installed rpm package
rpm -q package_name --whatrequires Show a list of dependencies with an rpm package
rpm -q package_name --whatprovides Display the volume occupied by an rpm package
rpm -q package_name --scripts Show scripts executed during install/remove
rpm -q package_name --changelog Display the modification history of an rpm package
rpm -qf /etc/httpd/conf/httpd.conf Confirm which rpm package provides the given file
rpm -qp package.rpm -l Show a list of files provided by an rpm package that has not been installed
rpm --import /media/cdrom/RPM-GPG-KEY Import public key digital certificate
rpm --checksig package.rpm Confirm the integrity of an rpm package
rpm -qa gpg-pubkey Confirm the integrity of all installed rpm packages
rpm -V package_name Check file size, permission, type, owner, group, MD5 check and last modified time
rpm -Va Check all installed rpm packages on the system - use with care
rpm -Vp package.rpm Confirm that an rpm package has not been installed
rpm2cpio package.rpm | cpio --extract --make-directories *bin* Run an executable from an rpm package
rpm -ivh /usr/src/redhat/RPMS/`arch`/package.rpm Install a built package from an rpm source
rpmbuild --rebuild package_name.src.rpm Build an rpm package from an rpm source
Linux Command - YUM Package Upgrader - (Fedora, RedHat and similar)< /a>
command code Notes
yum install package_name Download and install an rpm package
yum localinstall package_name.rpm A rpm package will be installed, using your own repositories to resolve all dependencies for you
yum update package_name.rpm Update all rpm packages installed in the current system
yum update package_name Update an rpm package
yum remove package_name Delete an rpm package
yum list List all packages installed on the current system
yum search package_name Search for packages in rpm repositories
yum clean packages Clean up rpm cache and delete downloaded packages
yum clean headers Remove all header files
yum clean all Delete all cached packages and headers
Linux commands — DEB packages (Debian, Ubuntu and similar)
command code Notes
dpkg -i package.deb Install/update a deb package
dpkg -r package_name Delete a deb package from the system
dpkg -l Display all deb packages installed in the system
dpkg -l | grep httpd Show all deb packages with "httpd" in their name
dpkg -s package_name Get information about a particular package already installed on the system
dpkg -L package_name Display the list of files provided by a deb package already installed in the system
dpkg --contents package.deb Display a list of files provided by a package that is not yet installed
dpkg -S /bin/ping Confirm which deb package provides the given file
Linux Commands — APT Software Tools (Debian, Ubuntu and similar)
command code Notes
apt-get install package_name Install/update a deb package
apt-cdrom install package_name Install/update a deb package from CD
apt-get update Update packages in the list
apt-get upgrade Upgrade all installed software
apt-get remove package_name Delete a deb package from the system
apt-get check Confirm that the dependent software warehouse is correct
apt-get clean Clean cache from downloaded packages
apt-cache search searched-package Return the package names containing the search string
Linux command — view file content
command code Notes
cat file1 View the content of the file forward from the first byte
tac file1 View the contents of a file in reverse from the last line
more file1 View the contents of a long file
less file1 Similar to the 'more' command, but it allows reverse operations in files as well as forward operations
head -2 file1 View the first two lines of a file
tail -2 file1 View the last two lines of a file
tail -f /var/log/messages Live view of content being added to a file
Linux Commands — Text Processing
command code Notes
cat file1 | command( sed, grep, awk, grep, etc...) > result.txt Merge the detailed description text of a file and write the introduction into a new file
cat file1 | command( sed, grep, awk, grep, etc...) >> result.txt Merge the detailed description text of a file and write the introduction into an existing file
grep Aug /var/log/messages Find keyword "Aug" in file '/var/log/messages'
grep ^Aug /var/log/messages Find words starting with "Aug" in file '/var/log/messages'
grep [0-9] /var/log/messages Select all lines containing numbers in the '/var/log/messages' file
grep Aug -R /var/log/* Search for the string "Aug" in the directory '/var/log' and subsequent directories
sed 's/stringa1/stringa2/g' example.txt Replace "string1" in the example.txt file with "string2"
sed '/^$/d' example.txt Remove all blank lines from the example.txt file
sed '/ *#/d; /^$/d' example.txt from example.txt Remove all comments and blank lines from the file
echo 'esempio' | tr '[:lower:]' '[:upper:]' Merge upper and lower cell contents
sed -e '1d' result.txt Exclude the first line from the file example.txt
sed -n '/stringa1/p' View lines that only contain the word "string1"
sed -e 's/ *$//' example.txt Delete whitespace at the end of each line
sed -e 's/stringa1//g' example.txt Remove only the term "string1" from the document and keep the rest
sed -n '1,5p;5q' example.txt View the content from the first line to the fifth line
sed -n '5p;5q' example.txt View line 5
sed -e 's/00*/0/g' example.txt Replace multiple zeros with a single zero
cat -n file1 Indicates the number of lines in the file
cat example.txt | awk 'NR%2==1' Delete all even lines in the example.txt file
echo a b c | awk '{print $1}' View the first column of a row
echo a b c | awk '{print $1,$3}' View the first and third columns of a row
paste file1 file2 Merge the contents of two files or two columns
paste -d '+' file1 file2 Merge the contents of two files or two columns, separated by "+" in the middle
sort file1 file2 Sort the contents of the two files
sort file1 file2 | uniq Take out the union of two files (only keep one duplicate line)
sort file1 file2 | uniq -u Delete intersection, leaving other rows
sort file1 file2 | uniq -d Take out the intersection of two files (leaving only files that exist in both files)
comm -1 file1 file2 Compare the contents of two files and delete only the content contained in 'file1'
comm -2 file1 file2 Compare the contents of two files and delete only the contents contained in 'file2'
comm -3 file1 file2 Comparing the contents of two files deletes only the parts common to both files
Linux command — character setting and file format conversion
command code Notes
dos2unix filedos.txt fileunix.txt Convert the format of a text file from MSDOS to UNIX
unix2dos fileunix.txt filedos.txt Convert a text file format from UNIX to MSDOS
recode ..HTML page.html Convert a text file to html
recode -l | more Show all allowed conversion formats
Linux command — file system analysis
command code Notes
badblocks -v /dev/hda1 Check for bad blocks on disk hda1
fsck /dev/hda1 Repair/check integrity of linux filesystem on disk hda1
fsck.ext2 /dev/hda1 Repair/check integrity of ext2 filesystem on disk hda1
e2fsck /dev/hda1 Repair/check integrity of ext2 filesystem on disk hda1
e2fsck -j /dev/hda1 Repair/check integrity of ext3 filesystem on disk hda1
fsck.ext3 /dev/hda1 Repair/check integrity of ext3 filesystem on disk hda1
fsck.vfat /dev/hda1 Repair/check the integrity of the fat filesystem on the hda1 disk
fsck.msdos /dev/hda1 Repair/check integrity of dos filesystem on disk hda1
dosfsck /dev/hda1 Repair/check integrity of dos filesystem on disk hda1
Linux command — initialize a file system
command code Notes
mkfs /dev/hda1 Create a file system on the hda1 partition
mke2fs /dev/hda1 Create a linux ext2 file system in the hda1 partition
mke2fs -j /dev/hda1 Create a linux ext3 (journal) file system in the hda1 partition
mkfs -t vfat 32 -F /dev/hda1 Create a FAT32 filesystem
fdformat -n /dev/fd0 Format a floppy disk
mkswap /dev/hda3 Create a swap filesystem
Linux command — SWAP file system
command code Notes
mkswap /dev/hda3 Create a swap filesystem
swapon /dev/hda3 Enable a new swap filesystem
swapon /dev/hda2 /dev/hdb3 Enable two swap partitions
Linux Commands — Backup
command code Notes
dump -0aj -f /tmp/home0.bak /home Make a full backup of the '/home' directory
dump -1aj -f /tmp/home0.bak /home Make an interactive backup of the '/home' directory
restore -if /tmp/home0.bak Restore an interactive backup
rsync -rogpav --delete /home /tmp Synchronize directories on both sides
rsync -rogpav -e ssh --delete /home ip_address:/tmp rsync via SSH tunnel
rsync -az -e ssh --delete ip_addr:/home/public /home/local Synchronize a remote directory to a local directory via ssh and zip
rsync -az -e ssh --delete /home/local ip_addr:/home/public Synchronize local directory to remote directory via ssh and compression
dd bs=1M if=/dev/hda | gzip | ssh user@ip_addr 'dd of=hda.gz' Execute an operation of backing up the local disk on the remote host through ssh
dd if=/dev/sda of=/tmp/file1 Back up disk contents to a file
tar -Puf backup.tar /home/user Perform an interactive backup of the '/home/user' directory
( cd /tmp/local/ && tar c . ) | ssh -C user@ip_addr 'cd /home/share/ && tar x -p' Copy a directory content in a remote directory via ssh
( tar c /home ) | ssh -C user@ip_addr 'cd /home/backup-home && tar x -p' Copy a local directory in a remote directory via ssh
tar cf - . | (cd /tmp/backup ; tar xf - ) Copy a directory to another place locally, retaining the original permissions and links
find /home/user1 -name '*.txt' | xargs cp -av --target-directory=/home/backup/ --parents Find and copy all files ending with '.txt' from one directory to another
find /var/log -name '*.log' | tar cv --files-from=- | bzip2 > log.tar.bz2 Find all files ending with '.log' and make a bzip package
dd if=/dev/hda of=/dev/fd0 bs=512 count=1 Do an action to copy the content of MBR (Master Boot Record) to floppy disk
dd if=/dev/fd0 of=/dev/hda bs=512 count=1 Restore MBR contents from a backup that has been saved to a floppy disk
Linux Commands — CD
command code Notes
cdrecord -v gracetime=2 dev=/dev/cdrom -eject blank=fast -force Empty a rewritable disc
mkisofs /dev/cdrom > cd.iso Create an iso image file of the CD on disk
mkisofs /dev/cdrom | gzip > cd_iso.gz Create a compressed disc iso image file on disk
mkisofs -J -allow-leading-dots -R -V "Label CD" -iso-level 4 -o ./cd.iso data_cd Create an iso image file of a directory
cdrecord -v dev=/dev/cdrom cd.iso Burn an ISO image
gzip -dc cd_iso.gz | cdrecord dev=/dev/cdrom - Burn a compressed ISO image
mount -o loop cd.iso /mnt/iso Mount an ISO image file
cd-paranoia -B Rip tracks from a CD to wav files
cd-paranoia -- "-3" Rip tracks from a CD to wav files (parameter -3)
cdrecord --scanbus Scan the bus to identify scsi channels
dd if=/dev/hdc | md5sum Verify the md5sum encoding of a device, such as a CD
Linux Commands - Network - (Ethernet and WIFI Wireless)
command code Notes
dhclient eth0 Enable the 'eth0' network device in dhcp mode
ethtool eth0 Display the traffic statistics of network card 'eth0'
host www.example.com Look up hostnames to resolve names and IP addresses and mirrors
hostname Display hostname
ifconfig eth0 Display the configuration of an ethernet card
ifconfig eth0 192.168.1.1 netmask 255.255.255.0 Control IP address
ifconfig eth0 promisc Set 'eth0' to promiscuous mode to sniff packets (sniffing)
ifdown eth0 Disable an 'eth0' network device
ifup eth0 Enable an 'eth0' network device
ip link show Display the connection status of all network devices
iwconfig eth1 Display the configuration of a wireless network card
iwlist scan Show wireless networks
mii-tool eth0 Display the connection status of 'eth0'
netstat -tup Display all enabled network connections and their PIDs
netstat -tup1 Display all listening network services and their PIDs
netstat -rn Display the routing table, similar to the "route -n" command
nslookup www.example.com Look up hostnames to resolve names and IP addresses and mirrors
route -n Show routing table
route add -net 0/0 gw IP Gateway Control Default Gateway
route add -net 192.168.0.0 netmask 255.255.0.0 gw 192.168.1.1 Control static route to network '192.168.0.0/16'
route del 0/0 gw IP gateway Delete static route
echo "1"> /proc/sys/net/ipv4/ip_foward Activate IP forwarding
tcpdump tcp port 80 Show all HTTP loopbacks
whois www.example.com Lookup in Whois database
Linux Commands — Microsoft Windows Networking
command code Notes
mount -t smbfs -o username=user,password=pass //WinClient/share/mnt/share Mount a windows network share
nbtscan ip addr netbios name resolution
nmblookup -A ip addr netbios name resolution
smbclient -L ip addr/hostname Display remote shares of a windows host
smbget -Rr smb://ip addr/share Ability to download files from a windows host via smb like wget
Linux command — IPTABLES(firewall)
command code Notes
iptables -t filter -L Show all links in the filter table
iptables -t nae -L Display all links of nat table
iptables -t filter -F Clear all rules based on the filter table
iptables -t nat -F Clear all rules based on nat table
iptables -t filter -X Delete all user-created links
iptables -t filter -A INPUT -p tcp --dport telnet -j ACCEPT Allow telnet access
iptables -t filter -A OUTPUT -p tcp --dport telnet -j DROP Block telnet access
iptables -t filter -A FORWARD -p tcp --dport pop3 -j ACCEPT Allow POP3 connections on the forwarding link
iptables -t filter -A INPUT -j LOG --log-prefix Record all packets blocked in the link
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE Set up a PAT (port address translation) to mask outgoing packets on eth0
iptables -t nat -A POSTROUTING -d 192.168.0.1 -p tcp -m tcp --dport 22-j DNAT --to-destination 10.0.0.2:22 Redirect packets destined for one host address to other hosts
Linux Commands — Monitoring and Debugging
command code Notes
free -m List RAM status in megabytes
kill -9 process id Forcibly close the process and end it
kill -1 process id Force a process to reload its configuration
last reboot Show reboot history
lsmod List the status of kernel modules
lsof -p process id List a list of files opened by the process
lsof /home/user1 List the open files in the given system directory
ps -eafw List linux tasks
ps -e -o pid,args --forest List linux tasks in a hierarchical manner
pstress Display programs in a tree view
smartctl -A /dev/hda Monitor hard disk device reliability by enabling SMART
smartctl -i /dev/hda Check if SMART of a hard disk device is enabled
strace -c ls >/dev/null List system calls made and receive with one process
strace -f -e open ls >/dev/null List library calls
tail /var/log/dmesg Display internal events during kernel boot
tail /val/log/messages Show system events
top List the linux tasks that use the most CPU resources
watch -nl 'cat /proc/interrupts' List real-time interrupts
Linux commands — other common commands
command code Notes
alias hh='history' Set an alias for the command history
apropos ...keyword Lists a list of commands including program keywords, especially useful when you only know what the program does, but don't remember the commands
chsh Change the shell command
chsh --list-shells Nice command to find out if you have to telnet to another machine
gpg -c filel Encrypt a file with GNU Privacy Guard
gpg filel.gpg Decrypt a file with GNU Privacy Guard
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