diff -uNr a/keksum/io.c b/keksum/io.c
--- a/keksum/io.c dca3567c27d22156d45bdbb018961469ec4ca2af26ed7efa3d060cc237088f1b3fb8bb2df50b627b8f0f24c1d1d7cd56f497d0f9f5a1330b8549c15d5ac76910
+++ b/keksum/io.c 86ff171be9d92e83b6de31f07902fad1d524ced59b796e6e3de2cbd230897e81a90fdc71a69ab667677f10b7d613b190688c223b7559c90505681b6fa3257350
@@ -8,6 +8,7 @@
 #include <unistd.h>
 #include "io.h"
 
+/* Write exactly len bytes from buf to fd, or die trying. */
 void write_all(int fd, char const *buf, size_t len) {
 	while (len) {
 		ssize_t n = write(fd,buf,len);
@@ -22,15 +23,16 @@
 	}
 }
 
-size_t read_all(int fd, unsigned char *buf, size_t len) {
+/* Read exactly len bytes from fd into buf, returning a short count only on EOF.
+ * On error, returns -1 and sets errno. */
+ssize_t read_all(int fd, unsigned char *buf, size_t len) {
 	size_t olen = len;
 	while (len) {
 		ssize_t n = read(fd,buf,len);
 		if (n <= 0) {
 			if (n) {
 				if (errno == EINTR) continue;
-				perr("read_all");
-				_exit(errno);
+				return -1;
 			}
 			break;
 		}
diff -uNr a/keksum/io.h b/keksum/io.h
--- a/keksum/io.h 64b3c8a8989834995dc2aa33bb1075a1dd53e8cb4f0e97847aaf8a8e2798f7b538d65af16bf656bf46de11126282b8c225f484df1e023123cb2b2437e5c7d676
+++ b/keksum/io.h 52f1007d12f5b605eb41509a12c799078020faf8b98202120321a1eec55c33b343670efc646c03baf0891b6f51aeb0ee4d76b11b9d08a496a60f963601ac665e
@@ -1,7 +1,7 @@
-#include <stddef.h>
+#include <sys/types.h>
 
 void write_all(int fd, char const *buf, size_t len);
-size_t read_all(int fd, unsigned char *buf, size_t len);
+ssize_t read_all(int fd, unsigned char *buf, size_t len);
 void write_str(int fd, char const *s);
 void newline(int fd);
 void write_line(int fd, char const *s);
diff -uNr a/keksum/keccak.c b/keksum/keccak.c
--- a/keksum/keccak.c 2d36c51a50632358041e360e0be17f698bc87dd8ca2bdfed48731991905444b0b687f11930d612a9debb3bdfc49439292e6695f2db05c04b92299ba6791b0c7f
+++ b/keksum/keccak.c 95fa68388a2b12bf22bbea2f42b65b9e95bbd70388b26d2dc75c051f07ffe3ef9dbb09255bc8ffca114352889a5a8ad88b940ff2e782712a1b4d46dc7382831a
@@ -253,8 +253,10 @@
 	write_all(1,buf,2*len);
 }
 
-/* Stream octets from stdin until EOF, then write hex to stdout. */
-void sponge(unsigned capacity, size_t out_bits) {
+/* Stream octets from stdin until EOF, then write hex to stdout.
+ * On success, returns 0.
+ * On read error, returns -1 and sets errno. */
+int sponge(unsigned capacity, size_t out_bits) {
 	static uint8_t buf[B/8];
 	unsigned rate = B - capacity,
 		 len = rate/8,
@@ -267,7 +269,14 @@
 
 	/* absorb */
 	reset();
-	while ((n = read_all(0,buf,len)) == len) {
+	for (;;) {
+		ssize_t nread = read_all(0,buf,len);
+		if (nread != len) {
+			if (nread < 0) return -1; /* read error */
+			/* else, end of file */
+			n = nread;
+			break;
+		}
 		load(buf,len);
 		keccakf();
 	}
@@ -292,6 +301,7 @@
 		keccakf();
 	}
 	extract(out_len);
+	return 0;
 }
 
 #ifdef TEST
diff -uNr a/keksum/main.c b/keksum/main.c
--- a/keksum/main.c d96e2cc71f3cad83002590418a194953719eab457b4084c05ccd4cd5b9051e6a2eef08581054451dd17f5558257473881434fdb90678e840fdfb63df03352f0a
+++ b/keksum/main.c 294be705c083b166c4aa10f3ea8a6333633af013374c5886d8e26db6ff45fba04e4b47c3a08857589130cd2c2c8ddb5415059ffb42f302c660614c701fa4db01
@@ -7,12 +7,12 @@
 #include <unistd.h>
 #include "io.h"
 
-void sponge(unsigned capacity, size_t out_bits);
+int sponge(unsigned capacity, size_t out_bits);
 
 #pragma GCC diagnostic ignored "-Woverlength-strings" /* wat. */
 
 static char const usage[] =
-"Usage: keksum [-c] [-sCAPACITY] [-nLENGTH] [-h] [--] [FILE]...\n"
+"Usage: keksum [-sCAPACITY] [-lLENGTH] [-h] [--] [FILE]...\n"
 "Compute KECCAK checksums.\n"
 "\n"
 "With no FILE, act as a filter, reading from standard input then printing\n"
@@ -20,7 +20,6 @@
 "name for each FILE.\n"
 "\n"
 "Options:\n"
-"  -c    read sums from FILEs and check them (TODO)\n"
 "  -l    set output length in bits (default 512)\n"
 "  -s    set sponge capacity in bits (default 256)\n"
 "  -h    print this help and exit\n"
@@ -99,21 +98,36 @@
 		usage_err("Capacity out of range");
 
 	if (argc) {
+		int status = 0;
+
 		/* Listing is similar to the GNU (?) format but with no input
 		 * mode character (you may know this as the mysterious extra
 		 * space): it's always binary. */
 		for (; argc; SHIFT) {
-			int fd = chkp(*argv, open(*argv, O_RDONLY));
+			int fd = open(*argv, O_RDONLY);
+			if (fd == -1) {
+				perr(*argv);
+				status = 1;
+				continue;
+			}
 			chkp("dup2", dup2(fd,0));
 			chkp("close", close(fd));
-			sponge(capacity,out_len);
+			if (sponge(capacity,out_len) == -1) {
+				perr(*argv);
+				status = 1;
+				continue;
+			}
 			write_str(1," ");
 			write_line(1,*argv);
 		}
+		return status;
 	}
 	else {
-		sponge(capacity,out_len);
+		if (sponge(capacity,out_len) == -1) {
+			perr("read");
+			return 1;
+		}
 		newline(1);
+		return 0;
 	}
-	return 0;
 }
diff -uNr a/keksum/manifest b/keksum/manifest
--- a/keksum/manifest bd1aec53bfa5828bce3f2058d8c3eefb87e29f2e269180a81a11beb2b83feb1e2f668116470390f10a41c393ba9b487fbd38a175633251ce27a7223f99824b70
+++ b/keksum/manifest 61ecfe7760cfb2333d926e8915f90dee52b2f1222016d6af8dfd2c73af3d9eeca6b3dfec3c677e5a5baa6d11928f7731b9d451110e8d9ca8953e93aa8ce4296c
@@ -1 +1,2 @@
 640981 keksum_subdir_genesis jfw Initial release (redone from keksum_genesis_3 to follow project subdir and manifest naming conventions) (redone from keksum_genesis for default capacity and test)
+832286 keksum_error_recovery_and_usage jfw Continue to next file rather than aborting on open or read errors. Fix glaring typo for the length option in the usage synopsis, and remove the tease about a -c option to check against a reference hash listing, which isn't planned to be done any time soon.