Learn about your system configuration using getconf

I recently learnt about a simple program named getconf that can be used to query and view values of various system configuration variables. It is a POSIX program that ships with the GNU C Library (glibc) and so should be available on any Linux system. It can be used to query system variables and path variables from the shell.

• To view all the variables and values that this program handles:

$ getconf -a

• To query a specific variable:

$ getconf INT_MAX

• Some of the getconf variables that I find interesting:

# Note: These are on my system. Values will vary on your system.

# Bits occupied by primitive types
CHAR_BIT                           8
LONG_BIT                           64

# Limits of signed types
CHAR_MAX                           127
CHAR_MIN                           -128
INT_MAX                            2147483647
INT_MIN                            -2147483648
SCHAR_MAX                          127
SCHAR_MIN                          -128
SHRT_MAX                           32767
SHRT_MIN                           -32768

# Biggest values of unsigned types
UCHAR_MAX                          255
UINT_MAX                           4294967295
ULONG_MAX                          18446744073709551615
USHRT_MAX                          65535

# Size of page in RAM & virtual memory
PAGE_SIZE                          4096

# Max length of host name (so short!)
HOST_NAME_MAX                      64

# Max length of login name
LOGIN_NAME_MAX                     256

# Bits used to store file sizes
FILESIZEBITS                       64

# Libc and pthread implementation details
GNU_LIBC_VERSION                   glibc 2.19
GNU_LIBPTHREAD_VERSION             NPTL 2.19

# The most interesting values!
# Cache details of your processor!
LEVEL1_ICACHE_SIZE                 32768
LEVEL1_ICACHE_ASSOC                8
LEVEL1_ICACHE_LINESIZE             64
LEVEL1_DCACHE_SIZE                 32768
LEVEL1_DCACHE_ASSOC                8
LEVEL1_DCACHE_LINESIZE             64
LEVEL2_CACHE_SIZE                  262144
LEVEL2_CACHE_ASSOC                 8
LEVEL2_CACHE_LINESIZE              64
LEVEL3_CACHE_SIZE                  8388608
LEVEL3_CACHE_ASSOC                 16
LEVEL3_CACHE_LINESIZE              64
LEVEL4_CACHE_SIZE                  0
LEVEL4_CACHE_ASSOC                 0
LEVEL4_CACHE_LINESIZE              0

• In case you are curious, getconf just calls the sysconf function provided by the GNU C Library. This can be seen in the posix/getconf.c source file in glibc.

• To get the cache details of an Intel 64-bit x86 CPU, sysconf uses the cpuid assembly instruction. This can be seen in the sysdeps/x86_64/cacheinfo.c source file in glibc.

Tried with: GLibC 2.19 and Ubuntu 14.04