Basic Linux Tools

Information about System Programs

  • man

  • whereis

  • whatis

  • mandb

  • which

# program man
man bash
man python3

man hosts # /etc/hosts config file man

man sshd # deamon man


man -k syslog # search man pages with "syslog"
apropos ssh # same as man -k

whatis bash
whatis node

whereis python3 # locate the sources, bins and mans of a prog

Working with Directories

  • pwd

  • cd

  • ls

  • mkdir

  • rmdir

# users home directory
cd ~

# parent directory
cd ..

# return to previous directory, and alternate between two Directories
cd -


# cd can be used in a subshell, as part of a pipeline.

echo $(cd /var/log && tail dmesg)
# or
echo $(cd /var/log; tail dmesg)


# this is especially useful with the tar utility, which relies on current shell pwd

( cd /bits/stage/; tar -c docs -f docs.tar; mv docs.tar ~; cd - )

Working with files

  • file: Determine Filetype

  • touch: update file timestamp

  • rm: Remove file or directory

  • mv: Move File or Directory

  • cp: Copy file or Directory

  • rename: rename many file with regex

  • cat: concatenate files and print to stdout

  • tac: reverse of cat - concatenate and print files in reverse

  • strings: display string within binary files.

  • xxd: make a hexdump or do the reverse

  • base64: make a base64 dump or do the reverse

  • man hier: distro’s file system hierarchy

# the s flag is for special file types typically found under dev
file /dev/*


# touch is to update or set timestamp of a file
touch ~/.bashrc


# cat can be used to concatenate multiple files. Like how we do with SSL certs
cat *.crt *.ca-bundle >> chain.crt


# to display ASCII text embedded within binary files
strings /bin/python3
string /bin/node

# human reasable hex dump with xxd
echo "I love Bash, C, Python and Javascript" | xxd -ps

# continueous hexdump
echo "I love Bash, C, Python and Javascript" | xxd -ps

# hex encode and decode pipeline with the -r reverse flag
echo "I love Bash, C, Python and Javascript" | xxd -ps | xxd -r -ps

# with cat and outiouput redirection
mkdir /tmp/mk; cat /var/log/dmesg | xxd -ps > /tmp/mk/dmesg.hex
tail /tmp/mk/dmesg.hex

# encode to base64 and back
echo "I love Bash, C, Python and Javascript" | base64 | base64 -d

The Linux Filesystem and conf

/etc/init.d/

Startup and Management scripts for system daemons and services.

less /etc/init.d/postgresql

/dev/

The /dev in-memory directory is populated with files as the kernel is recognising hardware. file -s /dev/*

/proc/

It is actually a view of the kernel, or better, what the kernel manages, and is a means to interact with it directly

cat /proc/cpuinfo

/etc/sysctl.conf

Runtime Kernel parameters. see also the sysctl command

Linux Processes

  • ps snapshop of the current processes

  • top and htop display linux process

  • jobs

  • time command to display real, sys and user time

time ls -lh | sort -k5n | less
time sudo ufw status