connection manager - what happens at startup & shutdown

Oracle Connection Manager (cman) is a great tool to create a gateway between networks which can not be connected, or filter those who can access to a service.
Most of the time, it's a very robust implementation and doesn't need a lot of attention. But if it's required to dig into it, a basic knowledge about it's components can be useful.


In this post I'll show what happens in a simple startup (& shutdown) of a mostly "default" cman.
The test was done on Oracle Linux 7.5 with cman 12.2.0.1.181016.

---

tl:dr

In my setup, processes are called this order.
at startup, cmctl spawns several processes. these processes communicate via sockets and has some shared memory segments

---

The details: 

The results in this post show some lines of interest cenerated by

strace -f -o <some_dir&gt>/cman_$$.strace -y -s 128 cman

and the 3 commands

administer cman_berx
startup
shutdown

Before each quote of the tracefile I write the line number - this is not an exact offset for your tests, just shows the sequence and sometimes big gaps which I do not show. I will name PIDs and executes together for better readability.

1:

10115 execve("<ORACLE_HOME>/bin/cmctl", ["cmctl"], [/* 118 vars */]) = 0

process 10115 is now cmctl.

200:

10115 open("<ORACLE_HOME>/env.ora", O_RDONLY) = 3
... 
10115 read(3, "# Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.\n# \n# NAME\n#   env.ora\n#\n# FUNCTION\n#   Oracle ENVironme"..., 4096) = 852

The undocumented file <ORACLE_HOME>/env.ora is checked for TNSNAMES_ORA parameter there - my file is default, so nothing is set there.

231:

10115 access("<TNS_ADMIN>/cman.ora", F_OK) = -1 ENOENT (No such file or directory)
10115 access("/etc/cman.ora", F_OK)     = -1 ENOENT (No such file or directory)
10115 access("<ORACLE_HOME>/network/admin/cman.ora", F_OK) = 0
10115 open("<ORACLE_HOME>/network/admin/cman.ora", O_RDONLY) = 3
... 
10115 read(3<<ORACLE_HOME>/network/admin/cman.ora>, "######################################################################\n#\n# Copyright (c) 2001,2002, Oracle Corporation. All righ"..., 4096) = 3996 
... 
10115 close(3<<ORACLE_HOME>/network/admin/cman.ora>) = 0 

10115 (cman) searches for cman.ora in <TNS_ADMIN> (nothing there) /etc (also nothing) and <ORACLE_HOME>/network/admin (there is an entry for cman_berx).

297:

10115 write(1</dev/pts/0>, "CMCTL> ", 7) = 7
10115 read(0</dev/pts/0>, "administer cman_berx\n", 1024) = 21

10115 (cmctl) writes a prompt (CMCTL>) and gets my command line command (administer cman_berx).

364:

10115 connect(4<socket:[1549779484]>, {sa_family=AF_INET, sin_port=htons(1522), sin_addr=inet_addr("x.y.z.78")}, 16) = -1 EINPROGRESS (Operation now in progress)

10115 (cmctl) tries to connect to the address:port provided in cman.ora - and can't connect. I assume that's the moment it realises it must start all related processes.


418:

10115 geteuid()                         = 5001
10115 clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x2b8713915150) = 10286
10115 rt_sigprocmask(SIG_BLOCK, [PIPE], NULL, 8) = 0
10286 set_robust_list(0x2b8713915160, 24 <unfinished ...>
10115 rt_sigaction(SIGPIPE, {0x2b8717669de0, ~[ILL TRAP ABRT BUS FPE SEGV USR2 TERM XCPU XFSZ SYS RTMIN RT_1], SA_RESTORER|SA_RESTART|SA_SIGINFO, 0x2b8718e9f680},  <unfinished ...>
10286 <... set_robust_list resumed> )   = 0
10115 <... rt_sigaction resumed> {SIG_DFL, [], 0}, 8) = 0
10115 rt_sigprocmask(SIG_UNBLOCK, [PIPE], NULL, 8) = 0
10286 clone( <unfinished ...>
10115 wait4(10286,  <unfinished ...>
10286 <... clone resumed> child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x2b8713915150) = 10287
10287 set_robust_list(0x2b8713915160, 24) = 0
10287 close(6<pipe:[1549773687]>)       = 0
10287 close(7<pipe:[1549773688]> <unfinished ...>
10286 exit_group(0)                     = ?
10287 <... close resumed> )             = 0
10287 setsid( <unfinished ...>
10286 +++ exited with 0 +++

10115 (cmctl) creates (clone) a new process (10286) - this process immediately clones another one (10287) and then terminates itself (exit_group). By this there is no parent-child relationship between 10115 (cmctl) and 10287. Still they both use the same binary (cmctl) and filehandles etc. - so 10287 closes some filehandles it doesn't require.

449:

10287 execve("/appl/oracle/product/cman_12201/bin/cmadmin", ["/appl/oracle/product/cman_12201/bin/cmadmin", "cman_berx", "-inherit"], [/* 119 vars */]) = 0

process 10287 is now cmadmin.


2602:

10287 access("/var/tmp/.oracle", F_OK)  = 0
10287 chmod("/var/tmp/.oracle", 01777)  = -1 EPERM (Operation not permitted)
10287 socket(AF_LOCAL, SOCK_STREAM, 0)  = 6<socket:[1549770245]>
...
10287 access("/var/tmp/.oracle_500100", F_OK) = -1 ENOENT (No such file or directory)
10287 mkdir("/var/tmp/.oracle_500100", 0700) = 0
10287 chmod("/var/tmp/.oracle_500100", 0700) = 0
10287 access("/var/tmp/.oracle_500100/s#10287.1", F_OK) = -1 ENOENT (No such file or directory)
10287 bind(6<socket:[1549770245]>, {sa_family=AF_LOCAL, sun_path="/var/tmp/.oracle_500100/s#10287.1"}, 110) = 0
10287 chmod("/var/tmp/.oracle_500100/s#10287.1", 0777) = 0
10287 listen(6<socket:[1549770245]>, 100) = 0
10287 getsockname(6<socket:[1549770245]>, {sa_family=AF_LOCAL, sun_path="/var/tmp/.oracle_500100/s#10287.1"}, [36]) = 0
10287 chmod("/var/tmp/.oracle_500100/s#10287.1", 0777) = 0 

10287 (cmadmin) checks if /var/tmp/.oracle exists and if it can change it's permission. In my environment the directory exists (as Grid Infrastructure is installed) but it's permissions can't be changed. It belongs to root.  Then /var/tmp/.oracle_500100 is created and a socket is created there. For easier readability, the PID is part of the socket name.

2631:

10287 clone(child_stack=0x2b6fd20de570, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x2b6fd20e99d0, tls=0x2b6fd20e9700, child_tidptr=0x2b6fd20e99d0) = 10289

10287 (cmadmin) creates another process (10289).

2701:

10287 <... clone resumed> child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x2b6fd1f80150) = 10290

10287 (cmadmin) creates another process (10290).

2719:

10290 <... clone resumed> child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x2b6fd1f80150) = 10291
...
10290 exit_group(0)                     = ?
...
10290 +++ exited with 0 +++

10290 creates 10291 and terminates itself.

2764:

10291 execve("/appl/oracle/product/cman_12201/bin/tnslsnr", ["/appl/oracle/product/cman_12201/bin/tnslsnr", "ifile=/appl/oracle/product/cman_12201/network/admin/cman.ora", "cman_berx", "-inherit", "-mode", "proxy"], [/* 119 vars */]) = 0

10291 becomes tnslsnr


3613:

10291 bind(11<socket:[1549780776]>, {sa_family=AF_INET, sin_port=htons(1522), sin_addr=inet_addr("0.0.0.0")}, 16) = 0
10291 listen(11<socket:[1549780776]>, 128) = 0
10291 getsockname(11<socket:[1549780776]>, {sa_family=AF_INET, sin_port=htons(1522), sin_addr=inet_addr("0.0.0.0")}, [16]) = 0

10291 (tnslsnr) listens on 0.0.0.0:1522 - But in cman.ora a specific IP address is given.

3669:

10291 write(12<<DIAG_DEST>/netcman/<hostname>/cman_berx/trace/cman_berx.log>, "Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=<server.domain>)(PORT=1522)))\n", 91) = 91

10291 (tnslsnr) writes something different to the logfile (?)

3674:

10291 access("/var/tmp/.oracle", F_OK)  = 0
10291 chmod("/var/tmp/.oracle", 01777)  = -1 EPERM (Operation not permitted)
10291 socket(AF_LOCAL, SOCK_STREAM, 0)  = 14<socket:[1549790968]>
10291 access("/var/tmp/.oracle/s#10291.1", F_OK) = -1 ENOENT (No such file or directory)
10291 bind(14<socket:[1549790968]>, {sa_family=AF_LOCAL, sun_path="/var/tmp/.oracle/s#10291.1"}, 110) = 0
10291 chmod("/var/tmp/.oracle/s#10291.1", 0777) = 0
10291 listen(14<socket:[1549790968]>, 1) = 0
10291 getsockname(14<socket:[1549790968]>, {sa_family=AF_LOCAL, sun_path="/var/tmp/.oracle/s#10291.1"}, [29]) = 0
10291 chmod("/var/tmp/.oracle/s#10291.1", 0777) = 0

10291 (tnslsnr) creates its own socket file for communication purpose.

4088:

10291 connect(16<socket:[1549778909]>, {sa_family=AF_LOCAL, sun_path="/var/tmp/.oracle/sprocr_local_conn_0_PROL"}, 110) = 0

4149:

10291 connect(15<socket:[1549778910]>, {sa_family=AF_LOCAL, sun_path="/var/tmp/.oracle/sCRSD_UI_SOCKET"}, 110) = 0

10291 (tnslsnr) checks some sockets which belong to Grid Infrastructure.

4616:

10291 clone(child_stack=0x2ac6b580b570, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x2ac6b58169d0, tls=0x2ac6b5816700, child_tidptr=0x2ac6b58169d0) = 10292

10291 (tnslsnr) creates PID 10292

4754:

10292 clone( <unfinished ...>
10291 <... close resumed> )             = 0
10292 <... clone resumed> child_stack=0x2ac6b584c570, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x2ac6b58579d0, tls=0x2ac6b5857700, child_tidptr=0x2ac6b58579d0) = 10293
10293 set_robust_list(0x2ac6b58579e0, 24 <unfinished ...>

10292 creates PID 10293

4790:

10293 exit(0)                           = ?
10292 <... poll resumed> )              = 1 ([{fd=15, revents=POLLIN}])
10293 +++ exited with 0 +++

10293 exits - it did not "clone" or "execve" anything

4841:

10287 shmget(0x59248000, 2462280, IPC_CREAT|IPC_EXCL|0600 <unfinished ...>

10287 (cmadmin) allocates a shared memory segment with key 0x59248000.

4937:

10287 <... clone resumed> child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x2b6fd1f80150) = 10294
...
10294 <... clone resumed> child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x2b6fd1f80150) = 10295
...
10294 exit_group(0)                     = ?
...
10294 +++ exited with 0 +++

10287 (cmadmin) creates PID 10294, this creates PID 10295 and terminates itself.


4967:

10295 execve("/appl/oracle/product/cman_12201/bin/cmgw", ["/appl/oracle/product/cman_12201/bin/cmgw", "cmgw0", "0", "16", "cman_berx", "SNLSM:59248000"], [/* 119 vars */]) = 0

10295 becomes cmgw0 - you can see the parameter SNLSM - it gives the shared memory key from 10287 (cmadmin).

5158:

10295 shmget(0x59248000, 1, 0)          = 2099576860

10295 (cmgw0) attaches to shared memory 10287 (cmadmin).


5566:

10287 <... clone resumed> child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x2b6fd1f80150) = 10296
...
10296 <... clone resumed> child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x2b6fd1f80150) = 10297
...
10296 exit_group(0)                     = ?

10287 (cmadmin) creates PID 10296 which creates 10297 and exits. - same as above

5625:

10297 execve("/appl/oracle/product/cman_12201/bin/cmgw", ["/appl/oracle/product/cman_12201/bin/cmgw", "cmgw1", "1", "16", "cman_berx", "SNLSM:59248000"], [/* 119 vars */] <unfinished ...>

10297 becomes cmgw1.

some (later) important sockets:
5680:

10295 connect(5<socket:[1549804554]>, {sa_family=AF_LOCAL, sun_path="/var/tmp/.oracle_500100/s#10287.1"}, 110 <unfinished ...>

6447:

10297 connect(5<socket:[1549798977]>, {sa_family=AF_LOCAL, sun_path="/var/tmp/.oracle_500100/s#10287.1"}, 110 <unfinished ...>

7448:

10295 bind(7<socket:[1549804555]>, {sa_family=AF_LOCAL, sun_path="/var/tmp/.oracle_500100/s#10295.1"}, 110 <unfinished ...>

7458:

10297 bind(7<socket:[1549798978]>, {sa_family=AF_LOCAL, sun_path="/var/tmp/.oracle_500100/s#10297.1"}, 110 <unfinished ...>

7896:

10115 connect(5<socket:[1549779550]>, {sa_family=AF_LOCAL, sun_path="/var/tmp/.oracle_500100/s#10287.1"}, 110 <unfinished ...> 

At this stage, cman is started, all processes are in memory and happy to server any requests.

---

The shutdown- command will be much faster:

8553:

10115 <... read resumed> "shutdown\n", 1024) = 9

10115 (cmctl) recieves "shutdown" from command line

8554

10115 write(5, "\0\0\0S\6$\0\0\0\0E\0\0\200\2\0\0\0\0\4\0\0\220_8\2\0\0\0\0\20\0#\0\0\000901A4C4F9FD8-3939-E034-0800208AB384\1\0v\0\0\0\3\0\0\0\0\0", 83) = 83

101115 (cmctl) informs 10287 (cmadmin)

8568:

10287 write(5<socket:[1549778933]>, "\0\0\0S\6 \0\0\0\0E\0\0\200\2\0\0\0\0\4\0\0p\344t\2\0\0\0\0\20\0#\0\0\00091986B2B10AC-3001-E034-0800208AB384\1\0l\0\0\0\1\0\0\0\0\0", 83) = 83
10287 times( <unfinished ...>
10295 <... epoll_wait resumed> [{EPOLLIN, {u32=13989488, u64=13989488}}], 1024, -1) = 1
10287 <... times resumed> NULL)         = 1269637186
10287 epoll_wait(7<anon_inode:[eventpoll]>,  <unfinished ...>
10295 read(5<socket:[1549804554]>, "\0\0\0S\6 \0\0\0\0E\0\0\200\2\0\0\0\0\4\0\0p\344t\2\0\0\0\0\20\0#\0\0\00091986B2B10AC-3001-E034-0800208AB384\1\0l\0\0\0\1\0\0\0\0\0", 8208) = 83
1

10287 (cmadmin) informs 10295 (cmgw0) (and later 10297 (cmgw1) by the same method) to shutdown

some cleanup takes place:

8585:

10295 unlink("/var/tmp/.oracle_500100/s#10295.1" <unfinished ...>

8590:

10295 rmdir("/var/tmp/.oracle_500100" <unfinished ...>

8621:

10297 unlink("/var/tmp/.oracle_500100/s#10297.1" <unfinished ...>

and all the processes terminate:

8869:

10289 exit(0)                           = ?
...
10289 +++ exited with 0 +++

8927:

10295 exit_group(0)                     = ?

8967:

10297 exit_group(0)                     = ?

9096:

10291 unlink("/var/tmp/.oracle/s#10291.1" <unfinished ...>

9293:

10291 exit_group(0)                     = ?

9305:

10287 exit_group(0)                     = ?

9321:

10115 exit_group(0)                     = ?

That's a simple startup and shutdown of connection manager - nothing fancy here, just a lot of processes and sockets which are created - and then deleted.

I hope you never need to read this article to it's end. But if you need to, it should provide some value for you!