Document exit codes for podman exec

Also fix podman run exit codes to show real messages when failures
happen.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

docs/podman-exec.1.md

@@ -52,6 +52,34 @@ The default working directory for running binaries within a container is the roo
 The image developer can set a different default with the WORKDIR instruction, which can be overridden
 when creating the container.
 
+## Exit Status
+
+The exit code from `podman exec` gives information about why the command within the container failed to run or why it exited.  When `podman exec` exits with a
+non-zero code, the exit codes follow the `chroot` standard, see below:
+
+**_125_** if the error is with podman **_itself_**
+
+    $ podman exec --foo ctrID /bin/sh; echo $?
+    Error: unknown flag: --foo
+    125
+
+**_126_** if the **_contained command_** cannot be invoked
+
+    $ podman exec ctrID /etc; echo $?
+    Error: container_linux.go:346: starting container process caused "exec: \"/etc\": permission denied": OCI runtime error
+    126
+
+**_127_** if the **_contained command_** cannot be found
+
+    $ podman exec ctrID foo; echo $?
+    Error: container_linux.go:346: starting container process caused "exec: \"foo\": executable file not found in $PATH": OCI runtime error
+    127
+
+**_Exit code_** of **_contained command_** otherwise
+
+    $ podman exec ctrID /bin/sh -c 'exit 3'
+    # 3
+
 ## EXAMPLES
 
 $ podman exec -it ctrID ls

docs/podman-run.1.md

@@ -902,28 +902,25 @@ the exit codes follow the `chroot` standard, see below:
 **_125_** if the error is with podman **_itself_**
 
     $ podman run --foo busybox; echo $?
-    # flag provided but not defined: --foo
-      See 'podman run --help'.
-      125
+    Error: unknown flag: --foo
+    125
 
 **_126_** if the **_contained command_** cannot be invoked
 
     $ podman run busybox /etc; echo $?
-    # exec: "/etc": permission denied
-      podman: Error response from daemon: Contained command could not be invoked
-      126
+    Error: container_linux.go:346: starting container process caused "exec: \"/etc\": permission denied": OCI runtime error
+    126
 
 **_127_** if the **_contained command_** cannot be found
 
     $ podman run busybox foo; echo $?
-    # exec: "foo": executable file not found in $PATH
-      podman: Error response from daemon: Contained command not found or does not exist
-      127
+    Error: container_linux.go:346: starting container process caused "exec: \"foo\": executable file not found in $PATH": OCI runtime error
+    127
 
 **_Exit code_** of **_contained command_** otherwise
 
     $ podman run busybox /bin/sh -c 'exit 3'
-    # 3
+    3
 
 ## EXAMPLES
 

docs/podman.1.md

@@ -103,24 +103,21 @@ the exit codes follow the `chroot` standard, see below:
 **_125_** if the error is with podman **_itself_**
 
     $ podman run --foo busybox; echo $?
-    # flag provided but not defined: --foo
-      See 'podman run --help'.
+    Error: unknown flag: --foo
       125
 
 **_126_** if executing a **_container command_** and the the **_command_** cannot be invoked
 
     $ podman run busybox /etc; echo $?
-    # exec: "/etc": permission denied
-      podman: Error response from daemon: Contained command could not be invoked
+    Error: container_linux.go:346: starting container process caused "exec: \"/etc\": permission denied": OCI runtime error
       126
 
 **_127_** if executing a **_container command_** and the the **_command_** cannot be found
     $ podman run busybox foo; echo $?
-    # exec: "foo": executable file not found in $PATH
-      podman: Error response from daemon: Contained command not found or does not exist
+    Error: container_linux.go:346: starting container process caused "exec: \"foo\": executable file not found in $PATH": OCI runtime error
       127
 
-**_Exit code_** of **_container command_** otherwise
+**_Exit code_** of **_contained command_** otherwise
 
     $ podman run busybox /bin/sh -c 'exit 3'
     # 3