Cmd.c32

Introduction

cmd.c32 executes its arguments as if they were typed-in directly at the Syslinux prompt. It is commonly used to reference other labels within a configuration file. It can also partially replace the need for a global append directive and/or variables in a cfg file. Let's see some examples.

The following code shows a typical boot menu.

UI menu.c32 LABEL normal LINUX bzImage INITRD initrd.img APPEND option_1 option_2 option_3 LABEL live LINUX bzImage INITRD initrd.img APPEND option_1 option_2 option_3 livemedia # The "live" label entry adds one additional option # in comparison to the "normal" label entry.

The following boot methods are equivalent alternatives:

• A_ Start the second entry in the above menu. Or,
• B_ Select the first entry in the above menu; press [TAB]; typing in " livemedia" results in something like ".linux bzImage initrd=initrd.img option_1 option_2 option_3 livemedia"; press [ENTER]. Or,
• C_ In a clean "boot:" prompt, type in "live"; [ENTER]. Or,
• D_ In a clean "boot:" prompt, type in "normal livemedia"; [ENTER].

Example (I)

The following label entry is also equivalent:

LABEL live COM32 cmd.c32 APPEND normal livemedia # Equivalent to typing "normal livemedia" in CLI.

By using cmd.c32 in the cfg file, editing the 'APPEND' line in the 'normal' boot entry will directly affect any other boot entry that includes 'cmd.c32 normal'.

Example (II)

The following cfg file:

UI menu.c32 LABEL normal LINUX bzImage INITRD initrd.img APPEND option_1 option_2 option_3 LABEL us LINUX bzImage INITRD initrd.img APPEND option_1 option_2 option_3 kbrd=us LABEL de LINUX bzImage INITRD initrd.img APPEND option_1 option_2 option_3 kbrd=de LABEL fr LINUX bzImage INITRD initrd.img APPEND option_1 option_2 option_3 kbrd=fr LABEL es LINUX bzImage INITRD initrd.img APPEND option_1 option_2 option_3 kbrd=es

is equivalent to:

UI menu.c32 LABEL normal LINUX bzImage INITRD initrd.img APPEND option_1 option_2 option_3 LABEL us COM32 cmd.c32 APPEND normal kbrd=us LABEL de COM32 cmd.c32 APPEND normal kbrd=de LABEL fr COM32 cmd.c32 APPEND normal kbrd=fr LABEL es COM32 cmd.c32 APPEND normal kbrd=es

Editing the second cfg file is simpler: just change the 'normal' boot entry.

Example (III)

Let's take the last boot entry from the above #Example (II):

 LABEL es
 COM32 cmd.c32
 APPEND normal kbrd=es

In the menu, select this entry and press [TAB] so as to edit the command line before acting on it. The CLI will show:

 >.com32 cmd.c32 normal kbrd=es 

which is shorter than the original:

>.linux bzImage initrd=initrd.img option_1 option_2 option_3 kbrd=es

This example shows one disadvantage of using cmd.c32. To get a command line such as:

>.linux bzImage initrd=initrd.img option_3 kbrd=es

the user needs to select the first entry, 'normal', press [TAB] and edit the whole command by deleting the unwanted options ('option_1 option_2') and typing in the additional wanted ones ('kbrd=es').

Example (IV)

More than one additional option can be added to the original label.

 LABEL live_fr
 COM32 cmd.c32
 APPEND normal livemedia kbrd=fr

Example (V)

Changing the INITRD is possible. Let's follow the explanation.

The 'normal' entry:

LABEL normal LINUX bzImage INITRD initrd.img APPEND option_1 option_2 option_3

is seen in CLI as:

>.linux bzImage initrd=initrd.img option_1 option_2 option_3

Since the last INITRD in a boot command overrides previous ones, then the following command (with an additional 'initrd=new.img'):

>.linux bzImage initrd=initrd.img option_1 option_2 option_3 initrd=new.img

is in fact equivalent to:

>.linux bzImage option_1 option_2 option_3 initrd=new.img

So the following entry in the cfg file:

LABEL new_initrd COM32 cmd.c32 APPEND normal initrd=new.img

uses 'initrd=new.img' instead of the original 'initrd=initrd.img'.

Example (VI)

Merging more than one INITRD is possible.

The command line:

>.linux bzImage option_1 option_2 option_3 initrd=initrd.img,new.img

uses both, initrd.img and new.img. The following entry is equivalent:

LABEL new_initrd_merged COM32 cmd.c32 APPEND normal initrd=initrd.img,new.img

since the original 'initrd=initrd.img' in 'normal' is "replaced" by the last 'initrd=initrd.img,new.img'.