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

  1. Print diagnostics messages to stderr and see systemd journal.

  2. Read entire message instead of 32 bytes (by read() or receive() in cycle)
  3. 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:

  1. Look at the last task: there's system programming here :)

  2. Create folder 09_Services2 at sugon.

  3. Put there the updated tcp_echo_serverSR.c file.

  4. 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

HSE/ArchitectureOS/Lab_09_Services2 (last edited 2020-06-22 10:24:38 by FrBrGeorge)