Note: In the following paragraphs, the "/" directory represents the root of the filesystem in which Syslinux (in its several variants) is (going to be) installed.
When booting, the initial working directory for SYSLINUX / ISOLINUX will be the directory containing the initial configuration file.
[-4.xx] If no initial configuration file is found, then SYSLINUX / EXTLINUX / ISOLINUX defaults to "/".
[5.00+] If no initial configuration file is found, then
SYSLINUX / ISOLINUX
defaults to the install-time working
directory (where "
ldlinux.* " is located).
When booting, the initial working directory for PXELINUX will be the parent directory of pxelinux.0 unless overridden with DHCP option 210. If no configuration file is found, then PXELINUX will start a timer to reboot the system in an attempt to restart the boot process and resolve a possible transient issue.
All (paths to) file names inside the configuration file are relative to the Working Directory, unless preceded with a slash. This is also valid for the command line interface.