> Well, I bit the bullet and fixed all of these warnings. Took me like two days of work, but now should be fine.
> You might want to test it again.

Done. Only 2 sprintf() overruns remain, see below.

> I only have gcc 9.2.0, there it compiles now without warning.

Ubuntu LTS 20.04 is GCC 9.3.0. (And incoming Debian-11 based Ubuntu LTS 22.04 likely to be GCC 10.something).

If you do not have access, I can create an account for you on daq00.triumf.ca.

daq00:elog$ make
c++ -O3 -funroll-loops -fomit-frame-pointer -W -Wall -Wno-deprecated-declarations -Wno-unused-result -Imxml -DHAVE_SSL -c -o mxml.o 
mxml/mxml.cxx
c++ -O3 -funroll-loops -fomit-frame-pointer -W -Wall -Wno-deprecated-declarations -Wno-unused-result -Imxml -DHAVE_SSL -w -c -o crypt.o 
src/crypt.cxx
c++ -O3 -funroll-loops -fomit-frame-pointer -W -Wall -Wno-deprecated-declarations -Wno-unused-result -Imxml -DHAVE_SSL -c -o strlcpy.o 
mxml/strlcpy.cxx
type git &> /dev/null; if [ $? -eq 1 ]; then REV="unknown" ;else REV=`git log -n 1 --pretty=format:"%ad - %h"`; fi; echo \#define 
GIT_REVISION \"$REV\" > src/git-revision.h
git is /usr/bin/git
c++ -O3 -funroll-loops -fomit-frame-pointer -W -Wall -Wno-deprecated-declarations -Wno-unused-result -Imxml -DHAVE_SSL -o elog 
src/elog.cxx mxml.o crypt.o strlcpy.o -lssl
c++ -O3 -funroll-loops -fomit-frame-pointer -W -Wall -Wno-deprecated-declarations -Wno-unused-result -Imxml -DHAVE_SSL -w -c -o auth.o 
src/auth.cxx
c++ -O3 -funroll-loops -fomit-frame-pointer -W -Wall -Wno-deprecated-declarations -Wno-unused-result -Imxml -DHAVE_SSL -o elogd 
src/elogd.cxx auth.o mxml.o crypt.o strlcpy.o -lssl
src/elogd.cxx: In function ‘void show_elog_list(LOGBOOK*, int, int, int, BOOL, char*)’:
src/elogd.cxx:21676:42: warning: ‘%s’ directive writing up to 149999 bytes into a region of size 1588 [-Wformat-overflow=]
21676 |                sprintf(str, "Time format %s", attr_list[i]);
      |                                          ^~
In file included from /usr/include/stdio.h:867,
                 from src/elogd.h:42,
                 from src/elogd.cxx:38:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:36:34: note: ‘__builtin___sprintf_chk’ output between 13 and 150012 bytes into a destination 
of size 1600
   36 |   return __builtin___sprintf_chk (__s, __USE_FORTIFY_LEVEL - 1,
      |          ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   37 |       __bos (__s), __fmt, __va_arg_pack ());
      |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/elogd.cxx:21660:42: warning: ‘%s’ directive writing up to 149999 bytes into a region of size 1588 [-Wformat-overflow=]
21660 |                sprintf(str, "Date format %s", attr_list[i]);
      |                                          ^~
In file included from /usr/include/stdio.h:867,
                 from src/elogd.h:42,
                 from src/elogd.cxx:38:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:36:34: note: ‘__builtin___sprintf_chk’ output between 13 and 150012 bytes into a destination 
of size 1600
   36 |   return __builtin___sprintf_chk (__s, __USE_FORTIFY_LEVEL - 1,
      |          ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   37 |       __bos (__s), __fmt, __va_arg_pack ());
      |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
c++ -O3 -funroll-loops -fomit-frame-pointer -W -Wall -Wno-deprecated-declarations -Wno-unused-result -Imxml -DHAVE_SSL -o elconv 
src/elconv.cxx -lssl



daq00:elog$ gcc -v
gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)