some linux notes

linux_notes.sh

ssh 10.0.4.3 -l jake

# read the manual pages - kind of like help
man
man cp # read the manual on the cp command
man 2 sync # gets you man page 2
manpath # where are man files located

<<'###ManPageSections'
1   User level commands and applications
2   System calls and kernel error codes
3   Library calls
4   Device drivers and network protocols
5   Standard file formats
6   Games and demonstrations
7   Miscellaneous files and documents
8   System administration commands
9   Obscure kernel specs and interfaces
###ManPageSections

<<'###FindingHelp'
Debian      debian.org/doc
Ubuntu      help.ubuntu.com
RHEL        redhat.com/docs
CentOS      wiki.centos.org
FreeBSD     freebsd.org/docs.html
###FindingHelp

# determine if binary is already in your search path
which cp # tells you where cp is

# whereis does a more broad search for a binary
whereis cp

# consults pre-compiled index of filesystem to locate filenames
locate signal.h

# system packaging
rpm
rpm -q python # checks if python is installed
rpm -qf /etc/httpd # checks which package file belongs to
dpkg-query -S /etc/apache2 #ubuntu method for finding package file belongs to
rpm -qa | wc -l # number of installed packages
rpm -ql python # shows you all installed files as part of the package

# installing things
sudo apt-get install tcpdump #ubuntu
sudo yum install tcpdump #rhel

# L - location
# o output to file
# s silent
curl -o /tmp/packageName -sL https://packagedownload.com
sudo sh /tmp/packageName

wget http://alink.com

# install updates
yum update kernel -y #auto answer yes to all questions

sudo -i
sudo -i -u username
su # root interactive shell - logs who became root
su -username # become a different user if you know the password
visudo # configure sudoers
visudo -c -f sudoers # validate the sudoers file

cut -d: -f1 /etc/passwd # list users

# boot order
efibootmgr
# o - explictily set boot order
sudo efibootmgr -o 0004,0002 # changing the boot order

#investigate status of systemd
systemctl # default is to list-units
systemctl list-units --type=service
systemctl list-unit-files --type=service
systemctl status -l dbus # checks status of specific unit
sudo systemctl enable dbus # enable a unit
sudo systemctl start dbus # start a unit
systemctl reboot # reboot
systemctl daemon-reload # reloads unit fules and systemd config
sudo systemctl isolate multi-user.target # switch system's current operating mode
systemctl get-default # how is server configured to boot?
sudo systemctl set-default multi-user.target # change boot method
systemctl list-units --type=target # show boot options
sudo systemctl add-wants multi-user.target my.local.service # add dependency

# setting up a new service
# put unit file in /etc/systemd/system
sudo systemctl enable custom.service

# systemd logging
journalctl # all log entries (oldest first)

# shutting down/rebooting
halt # system halt
halt -p # powers down
reboot # reboots
shutdown # warn logged on users - mostly obsolete

# processes
<<'###Signals'
1   HUP     Hangup
2   INT     Interrupt
3   QUIT    Quit
9   KILL    Kill                NO CATCH
10  BUS     Bus error
11  SEGV    Segmentation fault
15  TERM    Spftware termination
17  STOP    Stop                NO CATCH
18  TSTP    Keyboard Stop
19  CONT    Continue after stop
28  WINCH   Window changed
30  USR1    User Defined 1
31  USR2    User Defined 2
###Signals
ps # shows status of running processes
ps aux # <-- very useful
    # a - show all processes
    # x - even processes that don't have control terminal
    # u - user oriented format
ps auxww # show with all the info
ps aux | grep -v sshd # look up a single process
ps aux | grep -v grep | grep sshd # without grep return
pidof /usr/sbin/sshd # get pid of process
pgrep sshd # find pid of process
top # real time process info - task manager1
    # tap 1 to switch to core view
kill pid # default sends TERM (polite)
kill -9 pid # true KILL
sudo killall httpd # kills all apached web server processes
sudo pkill -u jake # kill processes found from user jake
sudo strace -p 586 # run a trace on a pid

# memory
vmstat

# FILES-FILES-FILES-FILES-FILES-FILES
<<'###FileType'
-       Regular File        editor,cp   rm
d       Directory           mkdir       rmdir, rm -r
c       Char Device File    mknod       rm
b       Block Device File   mknod       rm
s       Local Dom Socket
p       Named Pipe
l       Symolic Link        ln -s       rm
###FileType

<<'###lsbreakdown'
drwxr-xr-x. 2 root root 35 Feb 24 22:19 yo.service.d
d is for directory (1st)
rwxr permission bits
-xr setuid/setgid
x sticky bit
2 is hard link count - dir have at least 2
root = file owner
root = group owner
Feb 24 22:19 last modified
###lsbreakdown

file /tmp # basic info about a directory
file tmp.txt # basic info about a file

ls # list directory contents
ls -l tmp.txt # detailed info - determine ownership of a file
ls -l /tmp # detailed info on a directory
ls -i tmp.txt # identify inode number
ls -a # show all files in dir, even those with a .
ls -t # sort file by modification time
ls -F # diff between dir and exe
ls -R # list recursively
ls -h # file size in human-readable

cp # copy a file
cp names.csv /tmp # copy to /tmp

mv # move file

# making a new directory
sudo mkdir -p /yo/yo.service.d

# delete files
rm
rm -i tmp.txt # delete file with confirmation
# delete directory
rmdir yo
# delete a non-empty dir without confirmation
sudo rm -rf yo

# create symbolic links
sudo ln -s tmp /tmp/jake

# create and start editing a file
cat a.file # Get-Content of file
sudo bash -c 'cat > /tmp/try.yo'
cat example1 example2 example3 > example4

less a.file # browse a larger file
head a.file # fist 10 lines of text
head -n 20 a.file # first 20 lines of text
tail a.file # the last 10 lines of text

grep Alice a.file # find occurences of Alice in file
grep -v Alice a.File # all lines that don't contain Alice
grep -i Alice a.File # regardless cap

cut -f 3 -d"," # deal with csv's

# make a file executable
sudo chmod +x /tmp/a.file

lsof # lists all open files belonging to all active processes

<<'###chmod-encoding'
Octal   Binary  Perms
0       000     ---
1       001     --x
2       010     -w-
3       011     -wx

4       100     r--
5       101     r-x
6       110     rw-
7       111     rwx
###chmod-encoding
# user can read, write, execute. group can read, execute. others may read.
chmod u=rwx,g=rx,o=r tmp.txt
chmod a-x tmp.txt # removes execute from all categories
chmod g=u # makes group same as users
chmod --reference=filea fileb #makes fileb's mode same as filea's
chmod -R g+w mydir # recursively adds group write perm to mydir and all contents
find /tmp/yo/ -type f -exec chmod a-x {} ';' # adjust execute bits on just files

# change file ownership
sudo chown -R jake /tmp/jake # recursively change everything in this dir to owner jake

# change group ownership
chgrp

# eval file attribute flags
lsattr tst.txt

# change file attribute flags
chattr a tst.txt

# find just files
find /tmp/yo/ -type f

# FILES-FILES-FILES-FILES-FILES-FILES

# VIM-VIM-VIM-VIM-VIM-VIM-VIM-VIM-VIM
# yy    - yank (copy) a line
# dd    - delete (cut) a line
# p     - put (paste) the clipboard after cursor
# i     - insert before the cursor
# :wq or :x or ZZ - Write (save) and quit
# :q    - quit (fails if unsaved changes)
# :q! or ZQ - quit and throw away unsaved changes
# 0     - Start of line
# ^     - Start of line (after whitespace)
# $     - End of line
# gg    - first line
# G     - last line
# n     - next matching search pattern
# N     - previous match
# *     - next whole word under cursor
# #     - previous whole word under cursor
# u     - undo
# Ctrl+r - re-do
# VIM-VIM-VIM-VIM-VIM-VIM-VIM-VIM-VIM

# NANO-NANO-NANO-NANO-NANO-NANO-NANO
# Alt+6     - copy current line into cutbuffer
# Ctrl+K    - Cut current line into cutbuffer
# Ctrl+U    - Past contents of cutbuffer

# Ctrl+S    - Save current file
# Ctrl+O    - Offer to write file (save as)
# Ctrl+X    - Close buffer, exit Nano
# NANO-NANO-NANO-NANO-NANO-NANO-NANO

# crons & timers
# cron
crontab #filename install filename as your crontab
crontab -e # open a crontab in your editor
crontab -l # lists the contents of crontab
crontab -r # removes crontab
# systemd timers
systemctl list-timers # list timers
systmctl start systemd-tmpfiles-clean # manually run a scheduled task

# network
nmcli -p device # connection state info
nmcli con # uuid of connection info
nmcli con down id "eth0"
nmcli con up id "eth0"
nmcli con s id "eth0" # lots of info about the connection
nmcli con e id "eth0" # open in the interactive connection editor
# making changes manually in the file:
    cd /etc/sysconfig/network-scripts
    cat ifcfg-eth0
    nmcli connection reload
nmtui # graphic based editor

# disk stuff
sudo fdisk -l # get a list of disk info
mount # see all filesystems currently mounted
mount -o rw,remount / # re-mount a read-only file systems as read-write
sudo mount /tst/sda45 /users #installs file system on disk part /dev/sda4 under /users
unmount # detach filesystems

# see who is using a mountpoint currently
fuser -c /home # just the pids
fuser -cv /home # with user info

df -h # filesystem disk use
du -h # directories using space