07122022.md

1. More grep to dive in:

• grep -o: -o ~ --only-matching, print only the matched parts of a matching line, with each matched part on a separate output line.
• grep -A <NUM>: -A ~ --after-context, print <NUM> lines of trailing context after matching lines.
• grep -B <NUM>: -B ~ --before-context, print <NUM> lines of trailing context before matching lines.
• grep -C <NUM>: -C ~ --context, print <NUM> lines of output expanded in both up/down direction started from the matched context.

man ascii | grep -A 20 Tables

2. Services list of SysV and systemd:

• SysV services only (does not include the native systemd services):

chkconfig

• systemd services:

  • List all services:

  systemctl list-units
  systemctl list-unit-files
  systemctl list-units --type=service --state=active

  • List all services enabled on particular target: [target] can be found in the output of systemctl list-unit-files

  systemctl list-dependencies [target]
  systemctl list-dependencies sysinit.target

  • List of status reportation from a specific sercvice: (/dev/sda equivalent with and dev-sda.device and so on)

  systemctl status /dev/sda
  systemctl status dev-sda.device
  
  systemctl status /home
  systemctl status home.mount

• Some more systemctl options utilities:

systemctl list-jobs --all
systemctl list-sockets --all
systemctl list-timers --all

• The function splitPath is using only for current user profile, to see all system path, using:

systemd-path

• Retrieving log report from a service in a range of time:

journalctl --unit=home.mount --no-pager --since "1 week ago" | grep -i error
journalctl --unit=dev-sda.device --no-pager --since "1 week ago" | grep -i error

3. List of Escape Sequence:

+===================================================================+
| Escape Sequence | Unicode Character | Description                 |
+=================+===================+=============================+
|        \b       |       U+0008      | BS backspace                |
+-----------------+-------------------+-----------------------------+
|        \t       |       U+0009      | HT horizontal tab           |
+-----------------+-------------------+-----------------------------+
|        \n       |       U+000A      | LF line feed                |
+-----------------+-------------------+-----------------------------+
|        \f       |       U+000C      | FF form feed                |
+-----------------+-------------------+-----------------------------+
|        \r       |       U+000D      | CR carriage return          |
+-----------------+-------------------+-----------------------------+
|        \"       |       U+0022      | quotation mark              |
+-----------------+-------------------+-----------------------------+
|        \'       |       U+0027      | apostrophe                  |
+-----------------+-------------------+-----------------------------+
|        \/       |       U+002F      | slash (solidus)             |
+-----------------+-------------------+-----------------------------+
|        \\       |       U+005C      | backslash (reverse          |
|                 |                   | solidus)                    |
+-----------------+-------------------+-----------------------------+
|      \uXXXX     |       U+XXXX      | unicode character           |
+-----------------+-------------------+-----------------------------+

4. Process management:

• All of these signal process interaction command can be found in:

$ man 7 signal

Sending a signal
  The following system calls and library functions allow the caller to send a signal:

  raise(3)          Sends a signal to the calling thread.
  kill(2)           Sends a signal to a specified process, to all members of a specified process group, or to all processes on the system.
  killpg(2)         Sends a signal to all of the members of a specified process group.
  pthread_kill(3)   Sends a signal to a specified POSIX thread in the same process as the caller.
  tgkill(2)         Sends a signal to a specified thread within a specific process.  (This is the system call used to implement pthread_kill(3).)
  sigqueue(3)       Sends a real-time signal with accompanying data to a specified process.

• ps report snapshot of the current processes:

ps -fax
ps -aux
ps -ax -o %U%p%n%c

NOTE: the syntax %U%p%n%c corresponded with USER PID NI COMMAND.

• netstat: ss is the new version of netstat, lack some features, but exposes more TCP states and slightly faster.

netstat -tulpn | grep :22
ss -tulpn | grep 443

• -t - Show TCP ports.
• -u - Show UDP ports.
• -n - Show numerical addresses instead of resolving hosts.
• -l - Show only listening ports.
• -p - Show the PID and name of the listener’s process. This information is shown only if you run the command as root or sudo user.

• lsof: provides information about files opened by processes.

lsof -nP -iTCP -sTCP:LISTEN

• -n - Do not convert port numbers to port names.
• -p - Do not resolve hostnames, show numerical addresses.
• -iTCP -sTCP:LISTEN - Show only network files with TCP state LISTEN.

• Check connection to specific IP in Powershell:

telnet <IPv4> <Port>
tnc <Private IP> -port <Port number>