--- ckcdeb.h
+++ ckcdeb.h
@@ -1385,10 +1385,8 @@
 #endif /* NOPRINTFSUBST */
 
 #ifdef CKXPRINTF
-#define printf ckxprintf
-#define fprintf ckxfprintf
 #ifdef CK_ANSIC
-_PROTOTYP(int ckxprintf,(const char *, ...));
+_PROTOTYP(int ckxprintf,(const char *, ...) __attribute__ ((format (printf, 1, 2))));
 #ifdef NEXT
 _PROTOTYP(void ckxperror,(const char *));
 #else
@@ -1398,8 +1396,16 @@
 _PROTOTYP(int ckxperror,(const char *));
 #endif /* CK_SCOV5 */
 #endif /* NEXT */
-_PROTOTYP(int ckxfprintf,(FILE *, const char *, ...));
+_PROTOTYP(int ckxfprintf,(FILE *, const char *, ...) __attribute__ ((format (printf, 2, 3))));
 #endif /* CK_ANSIC */
+#ifdef printf
+#undef printf
+#endif
+#define printf ckxprintf
+#ifdef fprintf
+#undef fprintf
+#endif
+#define fprintf ckxfprintf
 #ifdef putchar
 #undef putchar
 #endif /* putchar */
--- ckcfns.c
+++ ckcfns.c
@@ -93,7 +93,7 @@
 #endif /* OS2ONLY */
 #endif /* OS2 */
 
-#ifdef VMS
+#if defined VMS || defined __linux__
 #include <errno.h>
 #endif /* VMS */
 
--- ckcnet.c
+++ ckcnet.c
@@ -173,6 +173,10 @@
 #endif /* CK_SOCKS5 */
 #endif /* CK_SOCKS */
 
+#ifdef __linux__
+#include <time.h>
+#endif
+
 #ifdef DEC_TCPIP
 #include <time.h>
 #include <inet.h>
--- ckufio.c
+++ ckufio.c
@@ -501,6 +501,10 @@
 _PROTOTYP( VOID ignorsigs, (void) );
 _PROTOTYP( VOID restorsigs, (void) );
 
+#ifdef __linux__
+#include <crypt.h>
+#endif
+
 /*
   Change argument to "(const char *)" if this causes trouble.
   Or... if it causes trouble, then maybe it was already declared
--- ckuus4.c
+++ ckuus4.c
@@ -34,8 +34,10 @@
 #include "ck_ssl.h"
 #endif /* CK_SSL */
 
-#ifdef VMS
+#if defined VMS || defined __linux__
 #include <errno.h>                      /* For \v(errno) */
+#endif
+#ifdef VMS
 extern char * ckvmserrstr(unsigned long);
 #ifndef OLD_VMS
 #include <lib$routines.h>               /* Not for VAX C 2.4 */
--- ckuus5.c
+++ ckuus5.c
@@ -22,7 +22,9 @@
 */
 
 /* Includes */
-
+#ifdef __linux__
+#include <errno.h>
+#endif
 #include "ckcdeb.h"
 #include "ckcasc.h"
 #include "ckcker.h"
--- ckuus6.c
+++ ckuus6.c
@@ -31,6 +31,9 @@
 #include <errno.h>
 #endif /* TCPSOCKET */
 #endif /* VMS */
+#ifdef __linux__
+#include <errno.h>
+#endif
 
 #ifdef datageneral
 #define fgets(stringbuf,max,fd) dg_fgets(stringbuf,max,fd)
--- ckuus7.c
+++ ckuus7.c
@@ -37,6 +37,9 @@
 #include <errno.h>
 #endif /* TCPSOCKET */
 #endif /* VMS */
+#ifdef __linux__
+#include <errno.h>
+#endif
 
 #ifdef OS2
 #ifndef NT
--- ckuusr.c
+++ ckuusr.c
@@ -87,6 +87,10 @@
 #define MULTINET_OLD_STYLE		/* Leave select prototype undefined */
 #endif /* MULTINET */
 
+#ifdef __linux__
+#include <errno.h>
+#endif
+
 #include "ckcdeb.h"
 #include "ckcasc.h"
 #include "ckcker.h"
--- ckuusx.c
+++ ckuusx.c
@@ -67,13 +67,13 @@
 _PROTOTYP(char * os2_gethostname, (void));
 #define getpid _getpid
 #endif /* OS2 */
-#ifdef BSD44
+#if defined BSD44 || __linux__
 #include <errno.h>
 #endif /* BSD44 */
 
 extern xx_strp xxstring;
 
-#ifdef OS2
+#if defined  OS2 || __linux__
 #include "ckcnet.h"
 #else /* OS2 */
 _PROTOTYP(int getlocalipaddr, (void));