09. Services, part 2.
Viewing system journal
Events in reverse order related to a particular unit:
andrewt@comp-core-i7-3615qm-0dbf32 ~ $ journalctl -r -u echosrv.service
Events in reverse order filtered with grep:
andrewt@comp-core-i7-3615qm-0dbf32 ~ $ journalctl -r | grep echosrv
Creating a service for hexdump
Create a service unit for hexdump:
andrewt@comp-core-i7-3615qm-0dbf32 ~ $ su - Password: comp-core-i7-3615qm-0dbf32 ~ # mcedit /etc/systemd/system/hexdump@.service
With the following content:
[Unit] Description=Hexdump service After=network.target [Service] Type=simple ExecStart=/usr/bin/hexdump -C StandardInput=socket [Install] WantedBy=default.target
Create a socket unit for hexdump:
comp-core-i7-3615qm-0dbf32 ~ # mcedit /etc/systemd/system/hexdump.socket
With the following content:
[Unit] Description=Soketizing Hexdump [Socket] ListenStream=1616 Accept=yes [Install] WantedBy=sockets.target
Verify the created service units:
comp-core-i7-3615qm-0dbf32 ~ # systemd-analyze verify hexdump@.service /lib/systemd/system/alteratord.socket:6: ListenStream= references a path below legacy directory /var/run/, updating /var/run/alteratord/.socket → /run/alteratord/.socket; please update the unit file accordingly. /lib/systemd/system/smb.service:10: PIDFile= references a path below legacy directory /var/run/, updating /var/run/smbd.pid → /run/smbd.pid; please update the unit file accordingly. /lib/systemd/system/winbind.service:9: PIDFile= references a path below legacy directory /var/run/, updating /var/run/winbindd.pid → /run/winbindd.pid; please update the unit file accordingly. /lib/systemd/system/nmb.service:10: PIDFile= references a path below legacy directory /var/run/, updating /var/run/nmbd.pid → /run/nmbd.pid; please update the unit file accordingly. /lib/systemd/system/chronyd.service:10: PIDFile= references a path below legacy directory /var/run/, updating /var/run/chrony/chronyd.pid → /run/chrony/chronyd.pid; please update the unit file accordingly.
Start the serice and check its status:
comp-core-i7-3615qm-0dbf32 ~ # systemctl start hexdump.socket
comp-core-i7-3615qm-0dbf32 ~ # systemctl status hexdump.socket
● hexdump.socket - Soketizing Hexdump
Loaded: loaded (/etc/systemd/system/hexdump.socket; disabled; vendor preset: disabled)
Active: active (listening) since Mon 2020-05-18 01:02:11 MSK; 1min 12s ago
Listen: [::]:1616 (Stream)
Accepted: 0; Connected: 0;
Tasks: 0 (limit: 2361)
Memory: 12.0K
CGroup: /system.slice/hexdump.socket
May 18 01:02:11 comp-core-i7-3615qm-0dbf32 systemd[1]: Listening on Soketizing Hexdump.See who is listening to sockets:
comp-core-i7-3615qm-0dbf32 ~ # netstat -ltp Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 *:netbios-ssn *:* LISTEN 2346/smbd tcp 0 0 localhost.localdomai:domain *:* LISTEN 2915/dnsmasq tcp 0 0 *:ssh *:* LISTEN 2075/sshd tcp 0 0 localhost.localdomain:ipp *:* LISTEN 2047/cupsd tcp 0 0 *:microsoft-ds *:* LISTEN 2346/smbd tcp 0 0 *:netbios-ssn *:* LISTEN 2346/smbd tcp 0 0 *:1616 *:* LISTEN 1/init tcp 0 0 localhost:domain *:* LISTEN 2915/dnsmasq tcp 0 0 *:ssh *:* LISTEN 2075/sshd tcp 0 0 localhost:ipp *:* LISTEN 2047/cupsd tcp 0 0 *:microsoft-ds *:* LISTEN 2346/smbd
Test the service:
comp-core-i7-3615qm-0dbf32 ~ # netcat localhost 1616 Hello World! 00000000 48 65 6c 6c 6f 20 57 6f 72 6c 64 21 0a |Hello World!.| 0000000d
While a connection is active, check service status:
comp-core-i7-3615qm-0dbf32 ~ # systemctl | grep hex hexdump@6-127.0.0.1:1616-127.0.0.1:53340.service loaded active running Hexdump service (127.0.0.1:53340) system-hexdump.slice loaded active active system-hexdump.slice hexdump.socket loaded active listening Soketizing Hexdump
Close the connection and check the status again:
comp-core-i7-3615qm-0dbf32 ~ # systemctl | grep hex system-hexdump.slice loaded active active system-hexdump.slice hexdump.socket loaded active listening Soketizing Hexdump
See systemd journal:
comp-core-i7-3615qm-0dbf32 ~ # journalctl -r -n 4 -- Logs begin at Sun 2020-04-19 06:24:19 MSK, end at Mon 2020-05-18 01:29:05 MSK. -- May 18 01:29:05 comp-core-i7-3615qm-0dbf32 systemd[1]: hexdump@8-127.0.0.1:1616-127.0.0.1:53344.service: Succeeded. May 18 01:29:02 comp-core-i7-3615qm-0dbf32 systemd[1]: Started Hexdump service (127.0.0.1:53344). May 18 01:28:42 comp-core-i7-3615qm-0dbf32 systemd[1]: hexdump@7-127.0.0.1:1616-127.0.0.1:53342.service: Succeeded. May 18 01:28:36 comp-core-i7-3615qm-0dbf32 systemd[1]: Started Hexdump service (127.0.0.1:53342).
Tasks: Modifying the TCP echo service
Print diagnostics messages to stderr and see systemd journal.
- Read entire message instead of 32 bytes (by read() or receive() in cycle)
Implement forking in the service so that it could handle multiple connections at the same time.
- Just leave the part of the program that reads from data socket to child process
and continue to accept connections in father process (with no wait() for the child).
H/W
Finish all the tasks:
Look at the last task: there's system programming here
Create folder 09_Services2 at sugon.
Put there the updated tcp_echo_serverSR.c file.
- Save systemd journal with events related to the services into text files and upload them to sugon. Hexdump service:
andrewt@comp-core-i7-3615qm-0dbf32 ~ $ journalctl -u hexdump*service > hexdump.journal
TCP echo service:andrewt@comp-core-i7-3615qm-0dbf32 ~ $ journalctl -u echosrv.service > echosrv.journal