Saturday Apr 23, 2016

Solaris 11: Few Random Commands

Logical Domains
Dependencies & Dependents
Network & Power Consumption Stats
HBA Listing


In the following example, dummy domain depends on two domains -- primary domain for virtual disks and virtual network devices, and dom2 for virtual disks and SR-IOV virtual functions (VF).

# ldm list-dependencies dummy
DOMAIN            DEPENDENCY        TYPE
dummy             primary           VDISK,VNET
                  dom2              VDISK,IOV

-l option displays the actual devices.


-r option in list-dependencies sub-command shows the dependents for the logical domain(s). -l option displays the actual devices in here too.


# ldm list-dependencies -r -l dom2
DOMAIN            DEPENDENT         TYPE           DEVICE
dom2              dummy             VDISK          primary-vds0/vdisk0:vol_dummy_disk0
                                    VDISK          service-vds0/vdisk0:vol_dummy_disk0
                                    IOV            /SYS/IOU1/PCIE14/IOVIB.PF0.VF1
                                    IOV            /SYS/IOU1/EMS4/CARD/NET0/IOVNET.PF0.VF1

Network Statistics

list-netstat sub-command in ldm utility displays the statistics for all the network devices that are configured in the domain(s).


# ldm ls-netstat dom2

NAME               IPACKETS     RBYTES       OPACKETS     OBYTES
----               --------     ------       --------     ------
net4               444.42M      61.27G       444.42M      7.12G
net1               13.20M       4989.22M     0            0
net0               0            0            0            0
ldoms-net0.vf1     37.62M       6.44G        49.15K       3.97M
ldoms-net0.vf0     523.34K      90.15M       62.85K       14.67M
ldoms-net1.vf15    0            0            0            0

List HBAs

list-hba sub-command in ldm utility lists out the physical SCSI HBA initiator ports in the target domain. -t option shows SCSI transport medium type such as FC or SAS.


# ldm ls-hba -t  primary
NAME                                                 VSAN
----                                                 ----
        init-port w5080020000016331
        Transport Protocol SAS
        init-port w5080020000016331
        Transport Protocol SAS

Check the latest man page for ldm(1M) for the complete list of options for those sub-commands.

Power Consumption Statistics

ldmpower command shows the breakdown of power consumed by processors and memory in different domains or in a given domain. Note that ldmpower is an independent command, not part of ldm utility.


# ldmpower -c processors -c memory -l primary
Processor Power Consumption in Watts
DOMAIN          15_SEC_AVG      30_SEC_AVG      60_SEC_AVG
primary         313             315             317

Memory Power Consumption in Watts
DOMAIN          15_SEC_AVG      30_SEC_AVG      60_SEC_AVG
primary         594             595             595

As usual, check the man page ldmpower(1M) for details.

PCI Devices

Scan & List

scanpci utility scans PCI buses and reports configuration settings for each PCI device that it finds.


# scanpci -v

pci bus 0x0002 cardnum 0x06 function 0x00: vendor 0x111d device 0x80ba
 Integrated Device Technology, Inc. [IDT] Device unknown
 CardVendor 0x0000 card 0x0000 (Card unknown)
  STATUS    0x0010  COMMAND 0x0147
  CLASS     0x06 0x04 0x00  REVISION 0x03
  BIST      0x00  HEADER 0x01  LATENCY 0x00  CACHE 0x10
  MAX_LAT   0x00  MIN_GNT 0x03  INT_PIN 0x00  INT_LINE 0x00
  Bus: primary=02, secondary=03, subordinate=72, sec-latency=0
  I/O behind bridge: 00000000-03ffffff
  Memory behind bridge: 00100000-2000ffff
  Prefetchable memory behind bridge: 100000000-777f0ffff

pci bus 0x0003 cardnum 0x00 function 0x00: vendor 0x8086 device 0x1521
 Intel Corporation I350 Gigabit Network Connection
 CardVendor 0x108e card 0x7b18 (Oracle/SUN, Quad Port GbE PCIe 2.0 Low Profile Adapter, UTP)
  STATUS    0x0010  COMMAND 0x0146
  CLASS     0x02 0x00 0x00  REVISION 0x01
  BIST      0x00  HEADER 0x80  LATENCY 0x00  CACHE 0x10
  BASE0     0x00100000 SIZE 1048576  MEM
  BASE3     0x00200000 SIZE 16384  MEM
  BASEROM   0x00280000 SIZE 524288
  MAX_LAT   0x00  MIN_GNT 0x00  INT_PIN 0x01  INT_LINE 0x00



Detect & Show Installed

Identifying Solaris 11 SRU level is one of the popular topics and it was covered in Solaris 11 documentation, My Oracle Support (MOS) and elsewhere by numerous bloggers. After all this, we still have to wonder why there isn't a conscious effort by the development team that owns pkg utility to make this a bit easier for normal human beings. In any case, pkg list entire or pkg info entire commands show a cryptic version string with a bunch of information encoded including the SRU level.

The second numeral in "branch" version represents the Solaris update whereas the third numeral is the SRU.


In the following example, Solaris update is 3 (running Solaris 11 - hence it is a Solaris 11.3 system) and current SRU is 5. (I underlined every alternate field)

# pkg info entire | grep -i branch


IDRs (Interim Diagnostic Reliefs) are in reality package updates whose names usually start with "idr" - therefore, just checking for the string "idr" in the list of installed packages on the system is sufficient to list out what IDRs were installed on the target system.

# pkg list idr*
pkg list: No packages matching 'idr*' installed <-- no IDRs installed

(Ticket Stub CSS Theme Credit: Kia Skretteberg)

Saturday Mar 26, 2016

Programming in C: Few Tidbits #6

[1] Case-insensitive String Comparison

strcasecmp() is the case-insensitive version of strcmp(). When building, make sure to include strings.h (note the plural form).

strncasecmp() is the counterpart to strncmp().

#include <string.h>
void main(int argc, char** argv)
        printf("\n\"%s\" and \"%s\" are ", argv[1], argv[2]);
        strcasecmp(argv[1], argv[2]) ? printf(" .. not identical") : printf(" .. identical");

% ./strcompare next NeXT
"next" and "NeXT" are  .. identical

[2] Initializing a Variable Length Array

As of the length of the variable length array is not known to the compiler at compile time, initializing a variable length automatic array with some default value usually results in a compilation error.

% cat -n varlen.c
     1  #include <stdlib.h>
     3  void main(int argc, char** argv) {
     4          int size=atoi(argv[1]);
     5          int array[size] = { 0 };
     6  }
/home/gmandali/C % cc -o varlen varlen.c
"varlen.c", line 5: variable length array can not be initialized: array
cc: acomp failed for varlen.c

One option is to explicitly initialize each element in the array to the desired default value.

% cat -n varlen.c
     1  #include <stdlib.h>
     3  void main(int argc, char** argv) {
     4          int size=atoi(argv[1]);
     5          int array[size];
     6          for (int i = 0; i < size; ++i)
     7                  array[i] = 0;
     8  }

% cc -o varlen varlen.c

Another option is to rely on memset().

% cat -n varlen.c
     1  #include <stdlib.h>
     2  #include <string.h>
     4  void main(int argc, char** argv) {
     5          int size=atoi(argv[1]);
     6          int array[size];
     7          memset(array, 0, sizeof(array));
     8  }

% cc -o varlen varlen.c

In this case, sizeof operator evaluates the operand (variable length array).

[3] Check if a Process is Alive

kill() function can be used to send a null signal (signal 0) to check the validity of a process.

% cat -n chkproc.c
     1  #include <sys/types.h>
     2  #include <signal.h>
     3  #include <stdlib.h>
     4  #include <stdio.h>
     6  void main(int argc, char **argv) {
     7          pid_t pid = atoi( argv[1] );
     8          int rc = kill( pid, 0 );
     9          if ( !rc ) {
    10                  printf("process with pid ( %d ) is alive", pid);
    11          } else {
    12                  printf("process with pid ( %d ) is not found", pid);
    13          }
    14  }

% cc -o chkproc chkproc.c

% ps
  PID TTY         TIME CMD
19846 pts/25      0:00 ps
28978 pts/25      0:00 bash

% ./chkproc 28978
process with pid ( 28978 ) is alive

% ./chkproc 28979
process with pid ( 28979 ) is not found

pid_t is actually int data type.

[4] Evaluating "( integer )" Expression

This is a simple one but probably an important one to remember. When dealing with an expression that yields an integer or when testing an integer, only a value of zero evaluates to false. Everything else including negative numbers, floating point numbers, characters, strings, .. are evaluated to true. In other words, anything non-zero is true.

% cat -n ifexpr.c
     1  #include <stdio.h>
     2  #include <stdlib.h>
     3  #include <ctype.h>
     5  void main(int argc, char **argv) {
     6          printf("\n[ %10d ] : %s",  0, (0) ? "true" : "false" );
     7          printf("\n[ %10d ] : %s",  1, (1) ? "true" : "false" );
     8          printf("\n[ %10d ] : %s",  -2, (-2) ? "true" : "false" );
     9          printf("\n[ %10s ] : %s",  "dummy", ("dummy") ? "true" : "false" );
    10          printf("\n[ %10c ] : %s",  'C', ('C') ? "true" : "false" );
    11          printf("\n[ %10f ] : %s",  2.34, (2.34) ? "true" : "false" );
    12          printf("\n[ %10f ] : %s\n",  0.0000, (0.0000) ? "true" : "false" );
    13  }

% cc -o ifexpr ifexpr.c
% ./ifexpr

[          0 ] : false
[          1 ] : true
[         -2 ] : true
[      dummy ] : true
[          C ] : true
[   2.340000 ] : true
[   0.000000 ] : false

[5] Variable Declaration in a switch { case: } Statement

Let's start with an example that shows compilation failure.

% cat -n varincase.c
     1  #include 
     3  void main() {
     4          switch ( 1 ) {
     5                  case 2:
     6                          int i = 15;
     7                          break;
     8                  default:
     9                          printf("default\n");
    10          }
    11  }

% cc -o varincase varincase.c
"varincase.c", line 6: syntax error before or at: int
"varincase.c", line 7: undefined symbol: i
cc: acomp failed for varincase.c

In this example, identifier i is being declared and initialized in the case label of switch statement. Since no linkage or no static scope was specified, identifier i will have automatic storage duration that is local to the block containing the invocation (switch() { .. }, that is).

However the problem with this code is that case <expression> and default are labels and the controlling expression in switch statement causes the control to jump to appropriate label. In the example, when the control is transferred to default label, it enters the scope of identifier i without initializing it [as it bypasses the case where the identifier is being declared and initialized], which is not permitted. Therefore the fix is to declare the identifier (if at all needed) in its own compound statement so the scope is limited to that compound statement. (A compond statement is a block of code.)

Adding curly braces around case 2: statements will make the code compile and run as shown below.

% cat -n varincase.c
     1  #include <stdio.h>
     3  void main() {
     4          switch ( 1 ) {
     5                  case 2:
     6                  {
     7                          int i = 15;
     8                          break;
     9                  }
    10                  default:
    11                          printf("default\n");
    12          }
    13  }

% cc -o varincase varincase.c

% ./varincase

Legible version of this post @

Friday Jan 29, 2016

[Solaris] Clock Synchronization, Max Username Length, Removable Media

Synchronize System Time with a Remote Host

One option is to rely on Network Time Protocol. If NTP is not available, rdate is an alternative to set the local system time to the time and date returned by the remote host (server).

  1. NTP

    # date
    Thu Jan 28 13:47:54 PST 2016
    # ntpdate	<-- is the NTP server within the network
    29 Jan 15:28:38 ntpdate[21143]: step time server offset 92435.318367 sec
    # date
    Fri Jan 29 15:28:42 PST 2016
  2. rdate


    • On server, ensure that time:stream service is online. If not, bring it online. server is the host that provides date/time.

      # ( svcs -H svc:/network/time:stream | grep online ) || \
      	( svcadm -v enable time:stream && svcadm -v enable time:dgram )
      svc:/network/time:stream enabled.
      svc:/network/time:dgram enabled.
    • On client, run: rdate <server>

      # date
      Thu Jan 28 13:54:37 PST 2016
      # rdate	<-- is just another host with the time service enabled.
      Fri Jan 29 15:41:47 2016
      # date
      Fri Jan 29 15:41:49 PST 2016

Listing Removable Media

.. such as CD-ROM, DVD-ROM and PCMCIA cards.

Related command: rmformat

# rmformat
Looking for devices...
     1. Logical Node: /dev/rdsk/c1t0d0s2
        Physical Node: /pci@304/pci@1/pci@0/pci@2/usb@0/storage@2/disk@0,0
        Connected Device: SUN      Remote ISO CDROM 1.01
        Device Type: CD Reader
        Bus: USB
        Size: 103.3 MB
        Access permissions: Medium is not write protected.
     2. Logical Node: /dev/rdsk/c2t0d0s2
        Physical Node: /pci@304/pci@2/usb@0/storage@1/disk@0,0
        Connected Device: VT       eUSB DISK        5206
        Device Type: Removable
        Bus: USB
        Size: 2.0 GB
        Access permissions: Medium is not write protected.

In addition to listing, the same command can also be used to format, label, partition removable & rewritable media.

rmmount and rmumount utilities can be used to mount and unmount removable or hot-pluggable volumes.


List the mountable device along with path(s)

# rmmount -l
/dev/dsk/c1t0d0s2    cdrom,cdrom0,cd,cd0,sr,sr0,CDROM,/media/CDROM

Man pages of rmformat(1) and rmmount(1).

Solaris Username Length

useradd command accepts usernames up to 32 characters. OS may warn beyond 8 characters - simply ignore if more than 8 characters is a requirement.

# useradd guyfawkes
UX: useradd: guyfawkes name too long.

# su guyfawkes

# id guyfawkes
uid=110(guyfawkes) gid=10(staff)

Directory Listing as a Tree

Check and install file/tree package if doesn't exist.

# ( pkg list -q file/tree ) || ( pkg install pkg:/file/tree )

List the directory using tree(1) command.

# tree -d /opt/SUNWldm
|-- bin
|   `-- schemas
|-- lib
|   |-- contrib
|   |-- ds
|   `-- templates
|-- man
|   |-- ja_JP.UTF-8
|   |   `-- man1m
|   `-- man1m
`-- platform
    `-- ORCL,SPARC64-X
        `-- lib
            `-- ds

14 directories

Wednesday Dec 30, 2015

[Solaris] Memory Blacklisting, Duplicate IP Address & Recovery, Group Package Installations, ..


Memory blacklist operation

To check if memory blacklist operation by LDoms Manager (ldm) is in progress, run:

echo "zeus ::print -a zeus_t mem_blacklist_inprog" | mdb -p `pgrep ldmd`

If no blacklist operation is in progress, the above may return output that is similar to:

<hex-address> mem_blacklist_inprog = 0 (false)

When a memory blacklist operation is in progress, the above may return output that is similar to:

<hex-address> mem_blacklist_inprog = 0x1 (true)

In such a situation, any attempt to run ldm commands related to memory management may fail with error:

A memory blacklist operation is being processed. Other memory operations are disabled until it completes

Sometimes a power cycle may clear the blacklist operation. In not-so-lucky situations, the affected DIMM(s) may have to be serviced.

(Credit: Eunice M.)


Duplicate IP Address & Recovery

If two nodes [running Solaris] on a network share the same IP address, Solaris kernel detects the duplicate address, marks it as duplicate and eventually disables and turns off the IP interface if the problem persists. These actions are typically recorded in the system log with warnings such as the following.

Dec 23 16:46:18 some-host ip: [ID 759807 kern.warning] WARNING: net0 has duplicate address xx.xx.xx.xx (in use by 00:10:e0:5d:9c:83); disabled
Dec 23 16:46:18 some-host in.routed[737]: [ID 238047 daemon.warning] interface net0 to xx.xx.xx.xx turned off

When the IP interface was disabled/turned off, ipadm show-if shows down state for that interface.

Once the problem was discovered and fixed [by the administrator or user] to avoid duplication of IP address, Solaris kernel enables and brings up the IP interface that it turned off earlier upon detecting a duplicate IP address. This action too is recorded in the system log.

Dec 23 16:51:18 some-host ip: [ID 636139 kern.notice] NOTICE: recovered address ::ffff:xx.xx.xx.xx on net0

Once the system marks an interface down due to the conflicting IP address in a remote system, the local system periodically checks to see if the conflict persists. In Solaris 11.3, the time between the checks is 300,000 milliseconds (300 seconds or 5 minutes). However in some cases waiting for 5 minutes might not be desirable. In such cases, the time between the duplicate IP address checks can be tuned by modifying the IP tunable parameter, _dup_recovery, to appropriate value.


Reduce the _dup_recovery value to 90 seconds.

  • Temporary change (non-persistent)

    # ndd -get /dev/ip ip_dup_recovery
    # ndd -set /dev/ip ip_dup_recovery 90000
    # ndd -get /dev/ip ip_dup_recovery
  • Permanent change (persistent across reboots)

    # ipadm show-prop -p _dup_recovery ip
    ip    _dup_recovery         rw   300000       --           300000       0-3600000
    # ipadm set-prop -p _dup_recovery=90000 ip
    # ipadm show-prop -p _dup_recovery ip
    ip    _dup_recovery         rw   90000        90000        300000       0-3600000

Notice the slight difference in parameter names when ndd and ipadm were used to tune the same value.


Solaris OS: What Group Package was Installed?

pkg list on target system shows this information.

# pkg list | grep "group/system/solaris" | grep server
group/system/solaris-minimal-server               0.5.11-     i--

List all packages that are part of the group package that was installed by running:

pkg list -as `pkg contents -r -H -o fmri -t depend -a type=group <group-package>`

List available group packages to install Solaris server:

# pkg search solaris-*-server | awk '{ print $3 "\t" $4}'
solaris/group/system/solaris-large-server       pkg:/group/system/solaris-large-server@0.5.11-
solaris/group/system/solaris-minimal-server     pkg:/group/system/solaris-minimal-server@0.5.11-
solaris/group/system/solaris-small-server       pkg:/group/system/solaris-small-server@0.5.11-
  • solaris-large-server provides an Oracle Solaris large server environment that contain all of the common network services that an enterprise server must provide. Hardware drivers that are required for servers such as InfiniBand drivers are also part of this group package.

  • solaris-small-server installs a smaller set of packages on a server and provides command-line environment

  • solaris-minimal-server installs the smallest possible set of Solaris packages which provides a minimal command-line environment

In addition to the above, solaris/group/system/solaris-desktop group package provides Solaris desktop environment. This package contains the GNOME desktop environment that includes GUI applications such as web browsers and mail clients, and drivers for graphics and audio devices.

Keep in mind that solaris-desktop group package has a lot more packages compared to the other three group packages outlined above.


Solaris OS: What AI Manifest was Used?

On target system, locate the AI manifest file that was used to perform the Solaris installation at:

  • /var/log/install/ai.xml

Installation log can also be found in the same directory.


Package History

pkg history shows command history related to a specific package or all packages installed on the system. This includes information such as who initiated the package operation, the complete command, how long it took to complete the operation, whether a new boot environment (BE) was created and the errors encountered, if any.

Refer to pkg(1) man page for the options and description.

Legible version of this post with full outputs @ [Solaris] Memory Blacklisting, Duplicate IP Address & Recovery, Group Package Installations, ..

Fancy Separator Credit: jkneb

Tuesday Sep 29, 2015

Solaris: Identifying EFI disks

EFI label supports physical disks and logical volumes that are > 2 TB in size. SMI support is limited to 2 TB.

Listed below are some of the characteristics and patterns that can help identify and differentiate an EFI labeled disk from a SMI labeled disk.

  • Device cxtxd0 [without any slice suffix] represents the entire disk

  • No cylinder information is stored in the EFI label.

  • No overlapping slices / partitions

    • eg.,

      EFI label disk:

      Notice that there are no overlapped partitions and no references to cylinders in the following prtvtoc output.

      % prtvtoc /dev/rdsk/c0t5000CCA04E0DEDD8d0
      * /dev/rdsk/c0t5000CCA04E0DEDD8d0 partition map
      * Dimensions:
      *     512 bytes/sector
      * 390721968 sectors
      * 390721901 accessible sectors
      * Flags:
      *   1: unmountable
      *  10: read-only
      * Unallocated space:
      *       First     Sector    Last
      *       Sector     Count    Sector
      *          34         6        39
      *   390070312    635239 390705550
      *                          First     Sector    Last
      * Partition  Tag  Flags    Sector     Count    Sector  Mount Directory
             0      4    00         40   2097152   2097191
             1      4    00    2097192 384827392 386924583
             4      4    00  386924584   3145728 390070311
             8     11    00  390705551     16384 390721934

      SMI label disk:

      Notice the overlapped partitions (0 & 2. also 2 & 6) and references to cylinders in the following prtvtoc output.

      # prtvtoc /dev/rdsk/c0t5000A72030082BD5d0s2
      * /dev/rdsk/c0t5000A72030082BD5d0s2 partition map
      * Dimensions:
      *     512 bytes/sector
      *      56 sectors/track
      *     224 tracks/cylinder
      *   12544 sectors/cylinder
      *   11429 cylinders
      *   11427 accessible cylinders
      * Flags:
      *   1: unmountable
      *  10: read-only
      *                          First     Sector    Last
      * Partition  Tag  Flags    Sector     Count    Sector  Mount Directory
             0      2    00          0    263424    263423
             1      3    01     263424    263424    526847
             2      5    01          0 143340288 143340287
             6      4    00     526848 142813440 143340287
  • Existence of /dev/[r]dsk/cxtxd0 implies EFI label. In case of SMI label, /dev/[r]dsk/cxtxd0 won't exist.

    • eg.,

      EFI label disk:

      % ls /dev/rdsk/c0t5000CCA04E0DEDD8d0

      SMI label disk:

      # ls /dev/rdsk/c0t5000A72030082BD5d0
      /dev/rdsk/c0t5000A72030082BD5d0: No such file or directory
  • The presence of "wd" (whole disk?) in device path of the physical device may imply EFI label.


    EFI label disk:

    % stat -c "%N" /dev/rdsk/c0t5000CCA04E0DEDD8d0
    ‘/dev/rdsk/c0t5000CCA04E0DEDD8d0’ -> ‘../../devices/scsi_vhci/disk@g5000cca04e0dedd8:wd,raw’

    SMI label disk:

    # stat -c "%N" /dev/rdsk/c0t5000A72030082BD5d0s2
    '/dev/rdsk/c0t5000A72030082BD5d0s2' -> '../../devices/scsi_vhci/disk@g5000a72030082bd5:c,raw'
  • As of this writing, devinfo(1M) does not support EFI labeled disks.

    • eg.,

      EFI label disk:

      % devinfo -i /dev/rdsk/c0t5000CCA04E0DEDD8d0
      devinfo: /dev/rdsk/c0t5000CCA04E0DEDD8d0: This operation is not supported on EFI labeled devices

      SMI label disk:

      # devinfo -i /dev/rdsk/c0t5000A72030082BD5d0s2
      /dev/rdsk/c0t5000A72030082BD5d0s2       0       0       12544   512     4

Credit: various internal sources

Tuesday Jun 30, 2015

Oracle Database : Profiling PL/SQL Code

AWR gathers and reports performance statistics that are useful in monitoring and tuning databases. Even though the combination of AWR/ASH reports and explain plans are very useful in analyzing the performance of queries, their usefulness is limited when dealing with PL/SQL-heavy applications. AWR and ASH reports help figure out if the database is spending significant amount of time and/or CPU cycles in executing PL/SQL code and in what PL/SQL modules -- however to identify performance bottlenecks withinin PL/SQL modules/routines and to pin-point hot spots in PL/SQL code at line level, DBMS_PROFILER, a database package, might be the right tool to use. Also check the documentation of DBMS_HPROF package out (Credit to guest for the tip/suggestion).

Rest of this post lists out the steps involved (on a high level) in generating the profile using DBMS_PROFILER; and subsequently generating a report or extracting relevant pieces of information.


  1. [Pre-11g env only] Create PLAN_TABLE as SYS user

    SQL> @?/rdbms/admin/utlxplan.sql
    SQL> GRANT ALL ON sys.plan_table TO public;
    SQL> CREATE PUBLIC SYNONYM plan_table FOR sys.plan_table;
  2. Create PL/SQL Profiler tables under the application schema

    As application user:

    SQL> @?/rdbms/admin/proftab.sql
  3. Install DBMS_PROFILER package as SYS user, if missing

    SQL> @?/rdbms/admin/profload.sql
  4. Start PL/SQL Profiler

    As application user:

  5. Execute one or more transactions to be profiled

  6. Stop the PL/SQL Profiler

    As application user:

  7. At this point, there are couple of options to analyze the profile.

    • Easy option - if you have access to My Oracle Support (MOS), download the profiler.sql from MOS Document ID 243755.1 "Script to produce HTML report with top consumers out of PL/SQL Profiler DBMS_PROFILER data", and execute.

      As application user:

      SQL> profiler.sql

      Select appropriate runid from the list displayed on stdout. profiler.sql script generates an HTML report that shows top time consumers for the duration of the execution of the PL/SQL Profiler run.

    • Not-so-Easy option - refer to the DBMS_PROFILER documentation to extract relevant information and details such as top time consumers, top lines sorted by total time, profiled PL/SQL module list, top modules etc.,

      Checking the documentation out for the following three key tables is a good start -- PLSQL_PROFILER_RUNS (information related to a profiling session), PLSQL_PROFILER_UNITS (information about each PL/SQL unit that was executed during the profiler session) and PLSQL_PROFILER_DATA (execution statistics for each line of code in PL/SQL units). Ancillary tables: DBA_SOURCE and PLAN_TABLE.

Thursday Apr 30, 2015

Few Random Solaris Commands : intrstat, croinfo, dlstat, fmstat, ..

Target: Solaris 11 and later. Some of these commands may work on earlier versions too.


Interrupt Statistics : intrstat utility

intrstat utility can be used to monitor interrupt activity generated by various hardware devices along with the CPU that serviced the interrupt and the CPU time spent in servicing those interrupts on a system. On a busy system, intrstat reported stats may help figure out which devices are busy at work, and keeping the system busy with interrupts.


.. [idle system] showing the interrupt activity on first two vCPUs ..

# intrstat -c 0-1 5

      device |      cpu0 %tim      cpu1 %tim
      cnex#0 |         0  0.0         0  0.0
      ehci#0 |         0  0.0         0  0.0
    hermon#0 |         0  0.0         0  0.0
    hermon#1 |         0  0.0         0  0.0
    hermon#2 |         0  0.0         0  0.0
    hermon#3 |         0  0.0         0  0.0
       igb#0 |         0  0.0         0  0.0
     ixgbe#0 |         0  0.0         0  0.0
   mpt_sas#0 |        18  0.0         0  0.0
      vldc#0 |         0  0.0         0  0.0

      device |      cpu0 %tim      cpu1 %tim
      cnex#0 |         0  0.0         0  0.0
      ehci#0 |         0  0.0         0  0.0
    hermon#0 |         0  0.0         0  0.0
    hermon#1 |         0  0.0         0  0.0
    hermon#2 |         0  0.0         0  0.0
    hermon#3 |         0  0.0         0  0.0
       igb#0 |         0  0.0         0  0.0
     ixgbe#0 |         0  0.0         0  0.0
   mpt_sas#0 |        53  0.2         0  0.0
      vldc#0 |         0  0.0         0  0.0

Check the outputs of the following as well.

# echo ::interrupts | mdb -k
# echo ::interrupts -d | mdb -k


Physical Location of Disk : croinfo & diskinfo commands

Both croinfo and diskinfo commands provide information about the chassis, receptacle, and occupant relative to all disks or a specific disk. Note that croinfo and diskinfo utilities share the same executable binary and function in a identical manner. The main difference being the defaults used by each of the utilities.


# croinfo
D:devchassis-path               t:occupant-type  c:occupant-compdev
------------------------------  ---------------  ---------------------
/dev/chassis//SYS/MB/HDD0/disk  disk             c0t5000CCA0125411FCd0
/dev/chassis//SYS/MB/HDD1/disk  disk             c0t5000CCA0125341F0d0
/dev/chassis//SYS/MB/HDD2       -                -
/dev/chassis//SYS/MB/HDD3       -                -
/dev/chassis//SYS/MB/HDD4/disk  disk             c0t5000CCA012541218d0
/dev/chassis//SYS/MB/HDD5/disk  disk             c0t5000CCA01248F0B8d0
/dev/chassis//SYS/MB/HDD6/disk  disk             c0t500151795956778Ed0
/dev/chassis//SYS/MB/HDD7/disk  disk             c0t5001517959567690d0

# diskinfo -oDcpd
D:devchassis-path               c:occupant-compdev     p:occupant-paths                                                               d:occupant-devices
------------------------------  ---------------------  -----------------------------------------------------------------------------  -----------------------------------------
/dev/chassis//SYS/MB/HDD0/disk  c0t5000CCA0125411FCd0  /devices/pci@400/pci@1/pci@0/pci@0/LSI,sas@0/iport@1/disk@w5000cca0125411fd,0  /devices/scsi_vhci/disk@g5000cca0125411fc
/dev/chassis//SYS/MB/HDD1/disk  c0t5000CCA0125341F0d0  /devices/pci@400/pci@1/pci@0/pci@0/LSI,sas@0/iport@2/disk@w5000cca0125341f1,0  /devices/scsi_vhci/disk@g5000cca0125341f0
/dev/chassis//SYS/MB/HDD2       -                      -                                                                              -
/dev/chassis//SYS/MB/HDD3       -                      -                                                                              -
/dev/chassis//SYS/MB/HDD4/disk  c0t5000CCA012541218d0  /devices/pci@700/pci@1/pci@0/pci@0/LSI,sas@0/iport@1/disk@w5000cca012541219,0  /devices/scsi_vhci/disk@g5000cca012541218
/dev/chassis//SYS/MB/HDD5/disk  c0t5000CCA01248F0B8d0  /devices/pci@700/pci@1/pci@0/pci@0/LSI,sas@0/iport@2/disk@w5000cca01248f0b9,0  /devices/scsi_vhci/disk@g5000cca01248f0b8
/dev/chassis//SYS/MB/HDD6/disk  c0t500151795956778Ed0  /devices/pci@700/pci@1/pci@0/pci@0/LSI,sas@0/iport@4/disk@w500151795956778e,0  /devices/scsi_vhci/disk@g500151795956778e
/dev/chassis//SYS/MB/HDD7/disk  c0t5001517959567690d0  /devices/pci@700/pci@1/pci@0/pci@0/LSI,sas@0/iport@8/disk@w5001517959567690,0  /devices/scsi_vhci/disk@g5001517959567690


Monitoring Network Traffic Statistics : dlstat command

dlstat command reports network traffic statistics for all datalinks or a specific datalink on a system.


# dlstat -i 5 net0
           net0  163.12M   39.93G  206.14M   43.63G
           net0      312  196.59K      146  370.80K
           net0      198  172.18K      121  121.98K
           net0      168   91.23K       93  195.57K

For the complete list of options along with examples, please consult the Solaris Documentation.


Fault Management : fmstat utility

Solaris Fault Manager gathers and diagnoses problems detected by the system software, and initiates self-healing activities such as disabling faulty components. fmstat utility can be used to check the statistics associated with the Fault Manager.

fmadm config lists out all active fault management modules that are currently participating in fault management. -m option can be used to report the diagnostic statistics related to a specific fault management module. fmstat without any option report stats from all fault management modules.


# fmstat 5
module             ev_recv ev_acpt wait  svc_t  %w  %b  open solve  memsz  bufsz
cpumem-retire            0       0  1.0 8922.5  96   0     0     0    12b      0
disk-diagnosis        1342       0  1.1 8526.0  96   0     0     0      0      0
disk-transport           0       0  1.0 8600.3  96   1     0     0    56b      0
zfs-diagnosis          139      75  1.0 8864.5  96   0     4    12   672b   608b
zfs-retire             608       0  0.0   15.2   0   0     0     0     4b      0

# fmstat -m cpumem-retire 5
                NAME VALUE            DESCRIPTION
           auto_flts 0                auto-close faults received
            bad_flts 0                invalid fault events received
     cacheline_fails 0                cacheline faults unresolveable
      cacheline_flts 0                cacheline faults resolved
    cacheline_nonent 0                non-existent retires
   cacheline_repairs 0                cacheline faults repaired
      cacheline_supp 0                cacheline offlines suppressed


InfiniBand devices : List & Show Information about each device

ibv_devices lists out all available IB devices whereas ibv_devinfo shows information about all devices or a specific IB device.


# ibv_devices
    device                 node GUID
    ------              ----------------
    mlx4_0              0021280001cee63a
    mlx4_1              0021280001cee492
    mlx4_2              0021280001cee4aa
    mlx4_3              0021280001cee4ea

# ibv_devinfo -d mlx4_0
hca_id: mlx4_0
        transport:                      InfiniBand (0)
        fw_ver:                         2.7.8130
        node_guid:                      0021:2800:01ce:e63a
        sys_image_guid:                 0021:2800:01ce:e63d
        vendor_id:                      0x02c9
        vendor_part_id:                 26428
        hw_ver:                         0xB0
        board_id:                       SUN0160000002
        phys_port_cnt:                  2
                port:   1
                        state:                  PORT_ACTIVE (4)
                        max_mtu:                2048 (4)
                        active_mtu:             2048 (4)
                        sm_lid:                 56
                        port_lid:               95
                        port_lmc:               0x00
                        link_layer:             IB

                port:   2
                        state:                  PORT_ACTIVE (4)
                        max_mtu:                2048 (4)
                        active_mtu:             2048 (4)
                        sm_lid:                 56
                        port_lid:               96
                        port_lmc:               0x00
                        link_layer:             IB

Other commands and utilities such as ibstatus, fwflash or cfgadm can also be used to retrieve similar information.


PCIe Hot-Plugging : hotplug command

When the hotplug service is enabled on a Solaris system, hotplug command to bring hot pluggable devices online or offline without physically adding or removing the device from the system.

The following command lists out the all physical [hotplug] connectors along with the current status.


# hotplug list -c
Connection           State           Description
IOU2-EMS2            ENABLED         PCIe-Native
IOU2-PCIE6           ENABLED         PCIe-Native
IOU2-PCIE7           EMPTY           PCIe-Native
IOU2-PCIE4           EMPTY           PCIe-Native
IOU2-PCIE1           EMPTY           PCIe-Native

For detailed instructions to hotplug a device, check the Solaris documentation out.

Fancy Separator Credit: jkneb

Tuesday Mar 31, 2015

Locality Group Observability on Solaris

Modern multi-socket servers exhibit NUMA characteristics that may hurt application performance if ignored. On a NUMA system (Non-uniform Memory Access), all memory is shared between/among processors. Each processor has access to its own memory - local memory - as well as memory that is local to another processor -- remote memory. However the memory access time (latency) depends on the memory location relative to the processor. A processor can access its local memory faster than the remote memory, and these varying memory latencies play a big role in application performance.

Solaris organizes the hardware resources -- CPU, memory and I/O devices -- into one or more logical groups based on their proximity to each other in such a way that all the hardware resources in a group are considered local to that group. These groups are referred as locality groups or NUMA nodes. In other words, a locality group (lgroup) is an abstraction that tells what hardware resources are near each other on a NUMA system. Each locality group has at least one processor and possibly some associated memory and/or IO devices. To minimize the impact of NUMA characteristics, Solaris considers the lgroup based physical topology when mapping threads and data to CPUs and memory.

Note that even though Solaris attempts to provide good performance out of the box, some applications may still suffer the impact of NUMA either due to misconfiguration of the hardware/software or some other reason. Engineered systems such as Oracle SuperCluster go to great lengths in setting up customer environments to minimize the impact of NUMA so applications perform as expected in a predictable manner. Still application developers and system/application administrators need to take NUMA factor into account while developing for and managing applications on large systems. Solaris provided tools and APIs can be used to observe, diagnose, control and even correct or fix the issues related to locality and latency. Rest of this post is about the tools that can be used to examine the locality of cores, memory and I/O devices.

Sample outputs are collected from a SPARC T4-4 server.

Locality Group Hierarchy

lgrpinfo prints information about the lgroup hierarchy and its contents. It is useful in understanding the context in which the OS is trying to optimize applications for locality, and also in figuring out which CPUs are closer, how much memory is near them, and the relative latencies between the CPUs and different memory blocks.


# lgrpinfo -a

lgroup 0 (root):
        Children: 1-4
        CPUs: 0-255
        Memory: installed 1024G, allocated 75G, free 948G
        Lgroup resources: 1-4 (CPU); 1-4 (memory)
        Latency: 18
lgroup 1 (leaf):
        Children: none, Parent: 0
        CPUs: 0-63
        Memory: installed 256G, allocated 18G, free 238G
        Lgroup resources: 1 (CPU); 1 (memory)
        Load: 0.0227
        Latency: 12
lgroup 2 (leaf):
        Children: none, Parent: 0
        CPUs: 64-127
        Memory: installed 256G, allocated 15G, free 241G
        Lgroup resources: 2 (CPU); 2 (memory)
        Load: 0.000153
        Latency: 12
lgroup 3 (leaf):
        Children: none, Parent: 0
        CPUs: 128-191
        Memory: installed 256G, allocated 20G, free 236G
        Lgroup resources: 3 (CPU); 3 (memory)
        Load: 0.016
        Latency: 12
lgroup 4 (leaf):
        Children: none, Parent: 0
        CPUs: 192-255
        Memory: installed 256G, allocated 23G, free 233G
        Lgroup resources: 4 (CPU); 4 (memory)
        Load: 0.00824
        Latency: 12

Lgroup latencies:

  |  0  1  2  3  4
0 | 18 18 18 18 18
1 | 18 12 18 18 18
2 | 18 18 12 18 18
3 | 18 18 18 12 18
4 | 18 18 18 18 12

CPU Locality

lgrpinfo utility shown above already provides CPU locality in a clear manner. Here is another way to retrieve the association between CPU ids and lgroups.

# echo ::lgrp -p | mdb -k

        1         0     17873        64      0-63
        2         0     17755        64      64-127
        3         0      2256        64      128-191
        4         0     18173        64      192-255

Memory Locality

lgrpinfo utility shown above shows the total memory that belongs to each of the locality groups. However, it doesn't show exactly what memory blocks belong to what locality groups. One of mdb's debugger command (dcmd) helps retrieve this information.

1. List memory blocks

# ldm list-devices -a memory

     PA                   SIZE            BOUND
     0xa00000             32M             _sys_
     0x2a00000            96M             _sys_
     0x8a00000            374M            _sys_
     0x20000000           1048064M        primary

2. Print the physical memory layout of the system

# echo ::syslayout | mdb -k

         STARTPA            ENDPA  SIZE  MG MN    STL    ETL
        20000000        200000000  7.5g   0  0      4     40
       200000000        400000000    8g   1  1    800    840
       400000000        600000000    8g   2  2   1000   1040
       600000000        800000000    8g   3  3   1800   1840
       800000000        a00000000    8g   0  0     40     80
       a00000000        c00000000    8g   1  1    840    880
       c00000000        e00000000    8g   2  2   1040   1080
       e00000000       1000000000    8g   3  3   1840   1880
      1000000000       1200000000    8g   0  0     80     c0
      1200000000       1400000000    8g   1  1    880    8c0
      1400000000       1600000000    8g   2  2   1080   10c0
      1600000000       1800000000    8g   3  3   1880   18c0

The values under MN column (memory node) can be treated as lgroup numbers after adding 1 to existing values. For example, a value of zero under MN translates to lgroup 1, 1 under MN translate to lgroup 2 and so on. Better yet, ::mnode debugger command lists out the mapping of mnodes to lgroups as shown below.

# echo ::mnode | mdb -k

     2075ad80000  0    1      -   249g   237g   114m   5.7g   714m      -
     2075ad802c0  1    2      -   240g   236g   288m    15g   4.8g      -
     2075ad80580  2    3      -   246g   234g   619m   9.6g   951m      -
     2075ad80840  3    4      -   247g   231g    24m     9g   897m      -

Unrelated notes:

  • Main memory on T4-4 is interleaved across all memory banks with 8 GB interleave size -- meaning first 8 GB chunk excluding _sys_ blocks will be populated in lgroup 1 closer to processor #1, second 8 GB chunk in lgroup 2 closer to processor #2, third 8 GB chunk in lgroup 3 closer to processor #3, fourth 8 GB chunk in lgroup 4 closer to processor #4 and then the fifth 8 GB chunk again in lgroup 1 closer to processor #1 and so on. Memory is not interleaved on T5 and M6 systems (confirm by running the ::syslayout dcmd). Conceptually memory interleaving is similar to disk striping.

  • Keep in mind that debugger commands (dcmd) are not committed - thus, there is no guarantee that they continue to work on future versions of Solaris. Some of these dcmds may not work on some of the existing versions of Solaris.

I/O Device Locality

-d option to lgrpinfo utility accepts a specified path to an I/O device and return the lgroup IDs closest to that device. Each I/O device on the system can be connected to one or more NUMA nodes - so, it is not uncommon to see more than one lgroup ID returned by lgrpinfo.


# lgrpinfo -d /dev/dsk/c1t0d0
lgroup ID : 1

# dladm show-phys | grep 10000
net4              Ethernet             up         10000  full      ixgbe0

# lgrpinfo -d /dev/ixgbe0
lgroup ID : 1

# dladm show-phys | grep ibp0
net12             Infiniband           up         32000  unknown   ibp0

# lgrpinfo -d /dev/ibp0
lgroup IDs : 1-4

NUMA IO Groups

Debugger command ::numaio_group shows information about all NUMA I/O Groups.

# dladm show-phys | grep up
net0              Ethernet             up         1000   full      igb0
net12             Ethernet             up         10     full      usbecm2
net4              Ethernet             up         10000  full      ixgbe0

# echo ::numaio_group | mdb -k
            ADDR GROUP_NAME                     CONSTRAINT
    10050e1eba48 net4                  lgrp : 1
    10050e1ebbb0 net0                  lgrp : 1
    10050e1ebd18 usbecm2               lgrp : 1
    10050e1ebe80 scsi_hba_ngrp_mpt_sas1  lgrp : 4
    10050e1ebef8 scsi_hba_ngrp_mpt_sas0  lgrp : 1

Relying on prtconf is another way to find the NUMA IO locality for an IO device.


# dladm show-phys | grep up | grep ixgbe
net4              Ethernet             up         10000  full      ixgbe0

== Find the device path for the network interface ==
# grep ixgbe /etc/path_to_inst | grep " 0 "
"/pci@400/pci@1/pci@0/pci@4/network@0" 0 "ixgbe"

== Find NUMA IO Lgroups ==
# prtconf -v /devices/pci@400/pci@1/pci@0/pci@4/network@0
    Hardware properties:
        name='numaio-lgrps' type=int items=1

Process, Thread Locality

  • -H of prstat command shows the home lgroup of active user processes and threads.

  • -h of ps command can be used to examine the home lgroup of all user processes and threads. -H option can be used to list all processes that are in a certain locality group.
            [Related] Solaris assigns a thread to an lgroup when the thread is created. That lgroup is called the thread's home lgroup. Solaris runs the thread on the CPUs in the thread's home lgroup and allocates memory from that lgroup whenever possible.

  • plgrp tool shows the placement of threads among locality groups. Same tool can be used to set the home locality group and lgroup affinities for one or more processes, threads, or LWPs.

  • -L option of pmap command shows the lgroup that contains the physical memory backing some virtual memory.
            [Related] Breakdown of Oracle SGA into Solaris Locality Groups

  • Memory placement among lgroups can possibly be achieved using pmadvise when the application is running or by using madvise() system call during development, which provides advice to the kernel's virtual memory manager. The OS will use this hint to determine how to allocate memory for the specified range. This mechanism is beneficial when the administrators and developers understand the target application's data access patterns.

    It is not possible to specify memory placement locality for OSM & ISM segments using pmadvise command or madvise() system call (DISM is an exception).


# prstat -H

  1865 root      420M  414M sleep    59    0 447:51:13 0.1%    2 java/108
  3659 oracle   1428M 1413M sleep    38    0  68:39:28 0.0%    4 oracle/1
  1814 oracle    155M  110M sleep    59    0  70:45:17 0.0%    4 gipcd.bin/9
     8 root        0K    0K sleep    60    -  70:52:21 0.0%    0 vmtasks/257
  3765 root      447M  413M sleep    59    0  29:24:20 0.0%    3 crsd.bin/43
  3949 oracle    505M  456M sleep    59    0   0:59:42 0.0%    2 java/124
 10825 oracle   1097M 1074M sleep    59    0  18:13:27 0.0%    3 oracle/1
  3941 root      210M  184M sleep    59    0  20:03:37 0.0%    4
  3743 root      119M   98M sleep   110    -  24:53:29 0.0%    1 osysmond.bin/13
  3324 oracle    266M  225M sleep   110    -  19:52:31 0.0%    4 ocssd.bin/34
  1585 oracle    122M   91M sleep    59    0  18:06:34 0.0%    3 evmd.bin/10
  3918 oracle    168M  144M sleep    58    0  14:35:31 0.0%    1 oraagent.bin/28
  3427 root      112M   80M sleep    59    0  12:34:28 0.0%    4 octssd.bin/12
  3635 oracle   1425M 1406M sleep   101    -  13:55:31 0.0%    4 oracle/1
  1951 root      183M  161M sleep    59    0   9:26:51 0.0%    4
Total: 251 processes, 2414 lwps, load averages: 1.37, 1.46, 1.47

== Locality group 2 is the home lgroup of the java process with pid 1865 == 

# plgrp 1865

    1865/1        2
    1865/2        2
    1865/22       4
    1865/23       4
    1865/41       1
    1865/42       1
    1865/60       3
    1865/61       3

# plgrp 1865 | awk '{print $2}' | grep 2 | wc -l

# plgrp 1865 | awk '{print $2}' | grep 1 | wc -l

# plgrp 1865 | awk '{print $2}' | grep 3 | wc -l

# plgrp 1865 | awk '{print $2}' | grep 4 | wc -l

== Let's reset the home lgroup of the java process id 1865 to 4 ==

# plgrp -H 4 1865
    1865/1        2 => 4
    1865/2        2 => 4
    1865/3        2 => 4
    1865/4        2 => 4
    1865/184      1 => 4
    1865/188      4 => 4

# plgrp 1865 | awk '{print $2}' | egrep "1|2|3" | wc -l

# plgrp 1865 | awk '{print $2}' | grep 4 | wc -l

# prstat -H -p 1865

  1865 root      420M  414M sleep    59    0 447:57:30 0.1%    4 java/108

== List the home lgroup of all processes ==

# ps -aeH
    0    0 ?           0:11 sched
    5    0 ?           4:47 zpool-rp
    1    4 ?          21:04 init
    8    0 ?        4253:54 vmtasks
   75    4 ?           0:13 ipmgmtd
   11    3 ?           3:09
   13    4 ?           2:45 svc.conf
 3322    1 ?         301:51 cssdagen
11155    3 ?           0:52 oracle
13091    4 ?           0:00 sshd
13124    3 pts/5       0:00 bash
24703    4 pts/8       0:00 bash
12812    2 pts/3       0:00 bash

== Find out the lgroups which shared memory segments are allocated from ==

# pmap -Ls 24513 | egrep "Lgrp|256M|2G"

         Address       Bytes Pgsz Mode   Lgrp Mapped File
0000000400000000   33554432K   2G rwxs-    1   [ osm shmid=0x78000047 ]
0000000C00000000     262144K 256M rwxs-    3   [ osm shmid=0x78000048 ]
0000000C10000000     524288K 256M rwxs-    2   [ osm shmid=0x78000048 ]
0000000C30000000     262144K 256M rwxs-    3   [ osm shmid=0x78000048 ]
0000000C40000000     524288K 256M rwxs-    1   [ osm shmid=0x78000048 ]
0000000C60000000     262144K 256M rwxs-    2   [ osm shmid=0x78000048 ]

== Apply MADV_ACCESS_LWP policy advice to a segment at a specific address ==

# pmap -Ls 1865 | grep anon

00000007DAC00000      20480K   4M rw---    4   [ anon ]
00000007DC000000       4096K    - rw---    -   [ anon ]
00000007DFC00000      90112K   4M rw---    4   [ anon ]
00000007F5400000     110592K   4M rw---    4   [ anon ]

# pmadvise -o 7F5400000=access_lwp 1865

# pmap -Ls 1865 | grep anon
00000007DAC00000      20480K   4M rw---    4   [ anon ]
00000007DC000000       4096K    - rw---    -   [ anon ]
00000007DFC00000      90112K   4M rw---    4   [ anon ]
00000007F5400000      73728K   4M rw---    4   [ anon ]
00000007F9C00000      28672K    - rw---    -   [ anon ]
00000007FB800000       8192K   4M rw---    4   [ anon ]


  • - Man pages of lgrpinfo(1), plgrp(1), pmap(1), prstat(1M), ps(1), pmadvise(1), madvise(3C),, mdb(1)
  • - Web search keywords: NUMA, cc-NUMA, locality group, lgroup, lgrp, Memory Placement Optimization, MPO

Credit: various internal and external sources

Saturday Feb 28, 2015

Programming in C: Few Tidbits #5

1. Splitting a long string into multiple lines

Let's start with an example. Here is a sample string. It'd be nice to improve readability by splitting it into multiple lines.

const char *quote = "The shepherd drives the wolf from the sheep's for which the sheep thanks the shepherd as his liberator, while the wolf denounces him for the same act as the destroyer of liberty. Plainly, the sheep and the wolf are not agreed upon a definition of liberty.";

Couple of ideas.

  • Line continuation: split the string anywhere at white space, and end the line with a backslash (\). Repeat until done.

    Backslash (\) is the continuation character often referred as backslash-newline.


    const char *quote = "The shepherd drives the wolf from the sheep's for which \
                            the sheep thanks the shepherd as his liberator, while \
                            the wolf denounces him for the same act as the destroyer \
                            of liberty. Plainly, the sheep and the wolf are not agreed \
                            upon a definition of liberty.";

    The C preprocessor removes the backslash and joins the following line with the current one. This is repeated until all lines are joined. However in the above example, indentation becomes part of the actual string thus a bunch of unwanted whitespaces appear in the final string. Besides, it is not possible to include comments at the end of any of those lines [after the line continuation character] if you ever wanted to. Both of these minor issues can be avoided with string literal concatenation (discussed next).

    Compiling the above with Solaris Studio C compiler results in the following output.

    The shepherd drives the wolf from the sheep's for which                         the sheep thanks the shepherd as his liberator, while                   the wolf denounces him for the same act as the destroyer             of liberty. Plainly, the sheep and the wolf are not agreed                      upon a definition of liberty.
  • String literal concatenation: split the string anywhere at white space, and end the line with a pair of quotes ("). Start the next line with quotes, and repeat until done.


    const char *quote = "The shepherd drives the wolf from the sheep's for which "         /* dummy comment */
                           "the sheep thanks the shepherd as his liberator, while "        // another dummy comment
                           "the wolf denounces him for the same act as the destroyer "
                           "of liberty. Plainly, the sheep and the wolf are not agreed "
                           "upon a definition of liberty.";

    Adjacent string literals are concatenated at compile time. Comments outside the string literals are ignored, and the concatenated string will not include indented whitespaces unless they are within the string literals (delimited by quotes).

    Printing the above results in the following output.

    The shepherd drives the wolf from the sheep's for which the sheep thanks the shepherd as his liberator, while the wolf denounces him for the same act as the destroyer of liberty. Plainly, the sheep and the wolf are not agreed upon a definition of liberty.

2. Simultaneous writing to multiple streams

The straight forward approach is to make multiple standard I/O library function calls to write to desired streams.


fprintf(stdout, "some formatted string");
fprintf(stderr, "some formatted string");
fprintf(filepointer, "some formatted string");

This approach may work well as long as there are only a few occurrences of such writing. However if there is a need to repeat it many times over the lifetime of a process, it can be simplified by wrapping all those function calls that write to different streams into a function so a single call to the wrapper function takes care of writing to different streams. If the number of arguments in the formatted string is not constant or not known in advance, one option is to make the wrapper function a variadic function so that it accepts a variable number of arguments. Here is an example.

The following example writes all messages to the log file, writes only informative messages to standard output (stdout) and writes only fatal errors to the high priority log. Without the logfmtstring() wrapper function, the same code would have had five different standard I/O library calls rather than just three that the sample code has.

% cc -o mstreams multstreams.c

% ./mstreams
[info] successful entries: 52. failed entries: 7

% cat app.log
[info] successful entries: 52. failed entries: 7
[fatal] billing system not available
[error] unable to ping internal system at

% cat app_highpriority.log
[fatal] billing system not available

Web search keywords: C Variadic Functions

3. Declaring variables within the scope of a CASE label in a SWITCH block

It is possible to declare and use variables within the scope of a case label with one exception -- the first statement after a case label should be a statement or an expression, but not a declaration. If not compiler throws an error during compilation such as the following.

The above failure can be fixed by either moving the variable declaration to any place after a valid statement if possible, or by adding a dummy or null statement right after the case label.


1. Move the declaration from right after the case label to any place after a valid statement.

/* works */
switch(NULL) {
                printf("\nin default ..");
                int cyear = 2015;
                printf("\nyear = %d", cyear);

2. Add a dummy or null statement right after the case label.

/* works */
switch(NULL) {
                ; // NULL statement
                int cyear = 2015;
                printf("\nin default ..");
                printf("\nyear = %d", cyear);

3. Yet another option is to define or create scope using curly braces ({}) for the case where variables are declared.

/* works too */
switch(NULL) {
                int cyear = 2015;
                printf("\nin default ..");
                printf("\nyear = %d", cyear);

Also see: Keyword – switch, case, default

(Full copy of the same blog post with complete examples can be found at:

Saturday Jan 31, 2015

Programming in C: Few Tidbits #4

1. Using Wildcards in Filename Pattern Matching

Relying on *stat() API is not much of an option when using wildcards to match a filename pattern. Some of the options involve traversing a directory checking each file for a match using fnmatch(), or to use system() function to execute an equivalent shell command. Another option that is well suited for this task is the glob*() API, which is part of Standard C Library Functions. (I believe glob() depends on fnmatch() for finding matches).

Here is a simple example that displays the number of matches found for pattern "/tmp/lint_" along with the listing of matches.

% ls -1 /tmp/lint_*

% cat match.c
#include <stdio.h>
#include <glob.h>

glob_t buf;

if (argc == 1) return 0;

glob(argv[1], 0 , NULL , &buf);

printf("\nNumber of matches found for pattern '%s': %d\n",
      argv[1], buf.gl_pathc);

for (int i = 0; i < buf.gl_pathc; ++i) {
    printf("\n\t%d. %s", (i + 1), buf.gl_pathv[i]);


% ./<executable> /tmp/lint_\*

Number of matches found for pattern '/tmp/lint_*': 7

        1. /tmp/lint_AAA.21549.0vaOfQ
        2. /tmp/lint_BAA.21549.1vaOfQ
        3. /tmp/lint_CAA.21549.2vaOfQ
        4. /tmp/lint_DAA.21549.3vaOfQ
        5. /tmp/lint_EAA.21549.4vaOfQ
        6. /tmp/lint_FAA.21549.5vaOfQ
        7. /tmp/lint_GAA.21549.6vaOfQ

Please check the man page out for details -- glob(3C).

2. Microtime[stamp]

One of the old blog posts has an example to extract the current timestamp using time API. It shows the timestamp in standard format month-date-year hour:min:sec. In this post, let's add microseconds to the timestamp.

Here is the sample code.

% cat microtime.c
#include <stdio.h>
#include <time.h>

char timestamp[80], etimestamp[80];
struct timeval tmval;
struct tm *curtime;

gettimeofday(&tmval, NULL);

curtime = localtime(&tmval.tv_sec);
if (curtime == NULL) return 1;

strftime(timestamp, sizeof(timestamp), "%m-%d-%Y %X.%%06u", curtime);
snprintf(etimestamp, sizeof(etimestamp), timestamp, tmval.tv_usec);

printf("\ncurrent time: %s\n", etimestamp);

% ./<executable>
current time: 01-31-2015 15:49:26.041111

% ./<executable>
current time: 01-31-2015 15:49:34.575214

One major change from old approach is the reliance on gettimeofday() since it returns a structure [timeval] with a member variable [tv_usec] to represent the microseconds.

strftime() fills up the date/time data in timestamp variable as per the specifiers used in time format (third argument). By the time strftime() completes execution, timestamp will have month-date-year hr:min:sec filled out. Subsequent snprintf fills up the only remaining piece of time data - microseconds - using the tv_usec member in timeval structure and writes the updated timestamp to a new variable, etimestamp.

Credit: stackoverflow user unwind.

3. Concatenating Multi-Formatted Strings

I have my doubts about this header - so, let me show an example first. The following rudimentary example attempts to construct a sentence that is something like "value of pi = (22/7) = 3.14". In other words, the sentence has a mixture of character strings, integers, floating point number and special characters.

% cat fmt.c
#include <stdio.h>
#include <string.h>

char tstr[48];
char pistr[] = "value of pi = ";
int num = 22, den = 7;
float pi = ((float)num/den);

char snum[8], sden[8], spi[8];

sprintf(sden, "%d", den);
sprintf(snum, "%d", num);
sprintf(spi, "%0.2f", pi);

strcpy(tstr, pistr);
strcat(tstr, "(");
strcat(tstr, snum);
strcat(tstr, "/");
strcat(tstr, sden);
strcat(tstr, ") = ");
strcat(tstr, spi);


% ./<executable>
value of pi = (22/7) = 3.14

Nothing seriously wrong with the above code. It is just that it uses a bunch of sprintf(), strcpy() and strcat() calls to construct the target string. Also it overallocates the memory required for the actual string.

The same effect can be achieved by using asprintf(). The resulting code will be much smaller and easy to maintain however. This function also eases the developer from the burden of allocating memory of appropriate size. In general, overallocation leads to memory wastage and underallocation likely leads to buffer overflows posing unnecessary security risks. When relying on asprintf(), developers are not relieved from two factors though -- checking the return value to see if the call succeeded, and in freeing up the buffer when done with it. Ignoring those two aspects lead to program failures in the worst case, and memory leaks are almost guaranteed.

Here is the alternate version that achieves the desired effect by making use of asprintf().

% cat ifmt.c
#include <stdio.h>
#include <stdlib.h>

char *tstr;
int num = 22, den = 7;
float pi = ((float)num/den);

int ret = asprintf(&tstr, "value of pi = (%d/%d) = %0.2f", num, den, pi);

if (ret == -1) return 1;


% ./<executable>
value of pi = (22/7) = 3.14

Also see: snprintf()

(Full copy of the same blog post with complete examples can be found at:


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