Linux LPI 117-101 # 6 Of 9

I want to show you one example, set | tee set.out | less. Here set
command generates the output and gives as an input to tee command. tee command
saves the output of set into set.out as well piping the output to less.

While killing the process using -9 signal it unable to clean up before exiting. When you
use the -9 signal, it sends the sigkill signal. Other Avaialble signals are:
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL
5) SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE
9) SIGKILL 10) SIGUSR1 11) SIGSEGV 12) SIGUSR2
13) SIGPIPE 14) SIGALRM 15) SIGTERM 17) SIGCHLD
18) SIGCONT 19) SIGSTOP 20) SIGTSTP 21) SIGTTIN
22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ
26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO
30) SIGPWR 31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1
36) SIGRTMIN+2 37) SIGRTMIN+3 38) SIGRTMIN+4 39) SIGRTMIN+5
40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8 43) SIGRTMIN+9
44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13
52) SIGRTMAX-12 53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9
56) SIGRTMAX-8 57) SIGRTMAX-7 58) SIGRTMAX-6 59) SIGRTMAX-5
60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2 63) SIGRTMAX-1
64) SIGRTMAX

nohup : run a command immune to hang-ups, with output to a
non-tty, to keep the process running after you logged out.

shutdown brings the system down in a secure way. All logged-in uers
are notified that the system is going to down, and login blocked.
shutdown -k message : Which sends the warning messages to all logged-in users.
shutdown -r time : Which reboots the system
shutdown -t time -h: Which halt the system after shutting down.

tee command redirect output to a file while still piping it to another
program.
Example: set | tee set.out | less : In example, output from set is written to file set.out
while also being piped to less.

Syntax of /etc/syslog.conf is :
facility.priority : Where facility represents facility of service and priority represents the
level of logs to store eg, info, err, emerg etc.

kill command is used to terminate the processes by default it sends the
TERM signal. When you send the -HUP signal, it will restart the process by reading
the original configuration file.

While killing the process, we can send the signal. By default kill
command sends the TERM signal, to send -9 signal
#kill -9 PID
While killing the process using -9 signal it unable to clean up before exiting.

Process can start either in foreground or in background. By default
commands executes on foreground. Running the process in foreground allows only
one command can enter at a time because we will get the shell to type another
command until fininshing the current command. But background process allows to
run the more than one command at a time.
To run the process in background just append the & at the end of the command.
Example:
# find / -name passwd >result &

runlevel command displays the current and previous runlevel.
Example:
[root@server1 ~]# runlevel
N 3
[root@server1 ~]#
Which means Currenct runlevel is 3 is runlevel is not changed.
Standard Runlevel
0 - halt (Do NOT set initdefault to this)
1 - Single user mode
2 - Multiuser, without NFS (The same as 3, if you do not have networking)
3 - Full multiuser mode
4 - unused
5 - X11
6 - reboot (Do NOT set initdefault to this)

Syslogd provides two system utilities which provide support for system
logging and kernel message trapping. Support of both internet and unix domain
sockets enables this utility packages to support both local and remote logging.

dmesg command prints the boot messages, you can check which
devices are detected by your kernel or not from the boot log messages.

/etc/syslog.conf is the syslog configuration file, where we specified the
facility and priority to send the facility related log messages to specified file.
kernel.warning /dev/console : this line sends the warning related to kernel into
/dev/console.

Facility in /etc/syslog.conf can be auth, authpriv, cron, daemon, kern,
lpr, mail, mark, news, security, syslog, user, uucp and local0. Where lpr is the
facility for line printer.

Explanation:
The top programs provides a dynamic real-time view of a running system. It can
display system summary information as well as a list of tasks currently being
mananged by the linux kernel.
-d interval : Delay Time : Specifies the delay between screen updates and overrides the
corresponding value in one personal configuration file or th startup default.

shutdown brings the system down in a secure way. All logged-in uers
are notified that the system is going to down, and login blocked.

Syntax: shutdown [time]
#shutdown -c : Which cancel the shutdown process.

/etc/syslog.conf is the syslog configuration file, where we specified the
facility and priority to send the facility related log messages to specified file.
kernel.warning /dev/console : this line sends the warning related to kernel into
/dev/console.

shutdown brings the system down in a secure way. All logged-in uers
are notified that the system is going to down, and login blocked.
Syntax: shutdown [time]
#shutdown -c : Which cancel the shutdown process.

The top program provides a dynamic real-time view of a running
system. It can display system summary information as well as a list of tasks
currently being managed by the Linux kernel. The types of system summary
information shown and the types, order and size of information displayed for tasks
are all user configurable and that configuration can be made persistent across
restarts.

To change the priority of running process we use the renice command.
Default priority is 0, highest priority is -20 and lowest priority is 19. The path of
renice command is /usr/bin/renice.

nohup : run a command immune to hang-ups, with output to a
non-tty, to keep the process running after you logged out.

when you enter the command it runs on foreground, which means you
can type the commands after completing only, this is called foregroup but when you
run the command in background, it allows to run multiple commands on same shell.
bg jobid: which runs the jobs in background
fg jobid: Which runs the jobs in foreground.

syslog is the daemon, which reads /etc/syslog.conf configuration file.
After changing the configuration of syslog.conf you should restart the syslog service.
# service syslog restart

Common Redirection Operators
Command >file : Redirects standard output of command into the file
Command>>file : Append the standard output of command into the file
Command Command 2>file : Redirects the standard Error into the file
And Pipe (|) is used to combine the command, in piping outout of first command goes as
input to the second command.
Answer D is correct because test command takes input from the Bill file and sends the
standard output to Certkiller command.

user facility represents the user processes Example:
User.* /var/log/userlogs : It sends all user processes logs into /var/log/userlogs file

> will save the output to result
>> will append the output to result
>& will copy the output to result

Facility in /etc/syslog.conf can be auth, authpriv, cron, daemon, kern,
lpr, mail, mark, news, security, syslog, user, uucp and local0. Where uucp facility
represents Unix to Unix copy.

Common Redirection Operators
Command >file : Redirects standard output of command into the file
Command>>file : Append the standard output of command into the file
Command Command 2>file : Redirects the standard Error into the file
And Pipe (|) is used to combine the command, in piping outout of first command goes as
input to the second command.
Answer A is correct because foo command takes input from the bar file and sends the
standard output to foobar command.

/etc/syslog.conf is the main log configuration file reads by syslogd
service. Which logs system messages on unix system.

Facility in /etc/syslog.conf can be auth, authpriv, cron, daemon, kern,
lpr, mail, mark, news, security, syslog, user, uucp and local0. Where mail facility
represents the mail processes . By default mail logs are send to /var/log/maillog file.

when you executes the program, it returns the exit code either 0 or
1-255. If returns the exit code 0 it means program executed successfully it it returns
non-zero values it means error occurred during executing the program.

-9 is the powerfull signal, which sends an unclean and immediate kill
signal to process ID.

user facility represents the user processes Example:
User.* /var/log/userlogs : It sends all user processes logs into /var/log/userlogs file

xinetd performs the same function as inetd: it starts programs that
provide Internet services. Instead of having such servers started at system
initialization time, and be format until a connection request arrives, xinetd is the
only daemon process started and it listens on all service ports ofr the services listed
in it's configuration file.

auth facility represents the user authentication processes, and
authentication related logs will send to /var/log/secure.

Jobs running on foregroud can suspend by pressing ctrl+z. Then
suspended job can be run either in foreground or in background. To run in
foregroud, fg command and to run in background bg command.
Or
bg job id
fg job id

kern facility represents the kernel processes, in first line of

/etc/syslog.conf file, you can see kern.* /dev/console, this means all kernel related log
messages will send to /dev/console.

Common Redirection Operators
Command >file : Redirects standard output of command into the file
Command>>file : Append the standard output of command into the file
Command Command 2>file : Redirects the standard Error into the file
And Pipe (|) is used to combine the command, in piping outout of first command goes as
input to the second command.
When we executes the command it generates the standard output as well as standard error
and displays in standard output (Terminal Window) is default. When we redirect the
standard error as well as standard output into the file, it will not send any output into the
terminal window.

Export sets the shell variable named TEST to snuffy.

news represents Usenet news example:
Uucp,news.crit /var/log/spooler This line represents the logs of news to redirect into the
/var/log/spooler log files.

When you send the kill command it by default sends the TERM signal.

The command kill sends the specified signal to the specified process or
process group. If no signal is specified, the TERM signal is sent.

Common Redirection Operators
Command >file : Redirects standard output of command into the file
Command>>file : Append the standard output of command into the file
Command Command 2>file : Redirects the standard Error into the file
And Pipe (|) is used to combine the command, in piping outout of first command goes as
input to the second command.
When we executes the command it generates the standard output as well as standard error
and displays in standard output (Terminal Window) is default. When we redirect the
standard error as well as standard output into the file, it will not send any output into the
terminal window.
myprog >file1.out 2>&1 : Where & works as a Logical AND Operator.

A is correct because to suspend the foreground job we use ctrl+z
keystroke. And it converts the foreground jobs in background in stopped status.
To display background job use: jobs command

kill command is used to terminate the processes by default it sends the
TERM signal. When you send the -HUP signal, it will restart the process by reading
the original configuration file.

You can see in /etc/syslog :
Cron.* /var/log/cron
This line represents that cron related all log messages will write into /var/log/cron file.

auth is the facility which represents the login processes. Either local
login or remote login, auth facilitiy traps the logs and writes into /var/log/secure file.

Process can start either in foreground or in background. By default
commands executes on foreground. Running the process in foreground allows only
one command can enter at a time because we will get the shell to type another
command until fininshing the current command. But background process allows to
run the more than one command at a time.
To run the process in background just append the & at the end of the command.
Example:
# find / -name passwd >result &
We can suspend the jobs running in foreground by pressing ctrl+z shortcut. As well as
can resume the suspended jobs either in background or foreground.
#fg %jobid : Runs the job in foreground
#bg %jobid : Runs the job in background
or
#fg command
#bg command

daemon facility represents the miscellaneous daemons like httpd,
vsftpd etc

You can see the timestamps on every log files this timestamps is
genereated by mark facility.