diff --git a/src/cli/common.rs b/src/cli/common.rs
index 355d76d12d..bc93025a57 100644
--- a/src/cli/common.rs
+++ b/src/cli/common.rs
@@ -522,3 +522,17 @@ pub fn report_error(e: &Error) {
         }
     }
 }
+
+pub fn ignorable_error(error: crate::errors::Error, no_prompt: bool) -> Result<()> {
+    report_error(&error);
+    if no_prompt {
+        warn!("continuing (because the -y flag is set and the error is ignorable)");
+        Ok(())
+    } else {
+        if confirm("\nContinue? (y/N)", false).unwrap_or(false) {
+            Ok(())
+        } else {
+            Err(error)
+        }
+    }
+}
diff --git a/src/cli/self_update.rs b/src/cli/self_update.rs
index 609cfdbd8a..3974f3376b 100644
--- a/src/cli/self_update.rs
+++ b/src/cli/self_update.rs
@@ -30,7 +30,7 @@
 //! Deleting the running binary during uninstall is tricky
 //! and racy on Windows.
 
-use crate::common::{self, Confirm};
+use crate::common::{self, ignorable_error, Confirm};
 use crate::errors::*;
 use crate::markdown::md;
 use crate::term2;
@@ -235,9 +235,16 @@ fn canonical_cargo_home() -> Result<String> {
 /// `CARGO_HOME`/bin, hard-linking the various Rust tools to it,
 /// and adding `CARGO_HOME`/bin to PATH.
 pub fn install(no_prompt: bool, verbose: bool, quiet: bool, mut opts: InstallOpts) -> Result<()> {
-    do_pre_install_sanity_checks()?;
+    if !env::var_os("RUSTUP_INIT_SKIP_EXISTENCE_CHECKS").map_or(false, |s| s == "yes") {
+        do_pre_install_sanity_checks(no_prompt)?;
+    }
+
     do_pre_install_options_sanity_checks(&opts)?;
-    check_existence_of_rustc_or_cargo_in_path(no_prompt)?;
+
+    if !env::var_os("RUSTUP_INIT_SKIP_EXISTENCE_CHECKS").map_or(false, |s| s == "yes") {
+        check_existence_of_rustc_or_cargo_in_path(no_prompt)?;
+    }
+
     #[cfg(unix)]
     do_anti_sudo_check(no_prompt)?;
 
@@ -378,25 +385,25 @@ fn check_existence_of_rustc_or_cargo_in_path(no_prompt: bool) -> Result<()> {
     // Only the test runner should set this
     let skip_check = env::var_os("RUSTUP_INIT_SKIP_PATH_CHECK");
 
-    // Ignore this check if called with no prompt (-y) or if the environment variable is set
-    if no_prompt || skip_check == Some("yes".into()) {
+    // Skip this if the environment variable is set
+    if skip_check == Some("yes".into()) {
         return Ok(());
     }
 
     if let Err(path) = rustc_or_cargo_exists_in_path() {
-        err!("it looks like you have an existing installation of Rust at:");
-        err!("{}", path);
-        err!("rustup should not be installed alongside Rust. Please uninstall your existing Rust first.");
-        err!("Otherwise you may have confusion unless you are careful with your PATH");
-        err!("If you are sure that you want both rustup and your already installed Rust");
-        err!("then please restart the installation and pass `-y' to bypass this check.");
-        Err("cannot install while Rust is installed".into())
-    } else {
-        Ok(())
+        warn!("it looks like you have an existing installation of Rust at:");
+        warn!("{}", path);
+        warn!("rustup should not be installed alongside Rust. Please uninstall your existing Rust first.");
+        warn!("Otherwise you may have confusion unless you are careful with your PATH");
+        warn!("If you are sure that you want both rustup and your already installed Rust");
+        warn!("then please reply `y' or `yes' or set RUSTUP_INIT_SKIP_PATH_CHECK to yes");
+        warn!("or pass `-y' to ignore all ignorable checks.");
+        ignorable_error("cannot install while Rust is installed".into(), no_prompt)?;
     }
+    Ok(())
 }
 
-fn do_pre_install_sanity_checks() -> Result<()> {
+fn do_pre_install_sanity_checks(no_prompt: bool) -> Result<()> {
     let rustc_manifest_path = PathBuf::from("/usr/local/lib/rustlib/manifest-rustc");
     let uninstaller_path = PathBuf::from("/usr/local/lib/rustlib/uninstall.sh");
     let rustup_sh_path = utils::home_dir().unwrap().join(".rustup");
@@ -412,7 +419,7 @@ fn do_pre_install_sanity_checks() -> Result<()> {
             "run `{}` as root to uninstall Rust",
             uninstaller_path.display()
         );
-        return Err("cannot install while Rust is installed".into());
+        ignorable_error("cannot install while Rust is installed".into(), no_prompt)?;
     }
 
     if rustup_sh_exists {
@@ -422,7 +429,10 @@ fn do_pre_install_sanity_checks() -> Result<()> {
         warn!("or, if you already have rustup installed, you can run");
         warn!("`rustup self update` and `rustup toolchain list` to upgrade");
         warn!("your directory structure");
-        return Err("cannot install while rustup.sh is installed".into());
+        ignorable_error(
+            "cannot install while rustup.sh is installed".into(),
+            no_prompt,
+        )?;
     }
 
     Ok(())
diff --git a/tests/cli-inst-interactive.rs b/tests/cli-inst-interactive.rs
index 93c8501943..53841283c1 100644
--- a/tests/cli-inst-interactive.rs
+++ b/tests/cli-inst-interactive.rs
@@ -8,6 +8,8 @@ use crate::mock::clitools::{
 };
 use crate::mock::{get_path, restore_path};
 use lazy_static::lazy_static;
+use rustup::utils::raw;
+use std::fs;
 use std::io::Write;
 use std::process::Stdio;
 use std::sync::Mutex;
@@ -39,9 +41,22 @@ pub fn setup(f: &dyn Fn(&Config)) {
 }
 
 fn run_input(config: &Config, args: &[&str], input: &str) -> SanitizedOutput {
+    run_input_with_env(config, args, input, &[])
+}
+
+fn run_input_with_env(
+    config: &Config,
+    args: &[&str],
+    input: &str,
+    env: &[(&str, &str)],
+) -> SanitizedOutput {
     let mut cmd = clitools::cmd(config, args[0], &args[1..]);
     clitools::env(config, &mut cmd);
 
+    for (key, value) in env.iter() {
+        cmd.env(key, value);
+    }
+
     cmd.stdin(Stdio::piped());
     cmd.stdout(Stdio::piped());
     cmd.stderr(Stdio::piped());
@@ -266,3 +281,104 @@ fn test_warn_if_complete_profile_is_used() {
         );
     });
 }
+
+fn create_rustup_sh_metadata(config: &Config) {
+    let rustup_dir = config.homedir.join(".rustup");
+    fs::create_dir_all(&rustup_dir).unwrap();
+    let version_file = rustup_dir.join("rustup-version");
+    raw::write_file(&version_file, "").unwrap();
+}
+
+#[test]
+fn test_prompt_fail_if_rustup_sh_already_installed_reply_nothing() {
+    setup(&|config| {
+        create_rustup_sh_metadata(&config);
+        let out = run_input(config, &["rustup-init"], "\n");
+        assert!(!out.ok);
+        assert!(out
+            .stderr
+            .contains("warning: it looks like you have existing rustup.sh metadata"));
+        assert!(out
+            .stderr
+            .contains("error: cannot install while rustup.sh is installed"));
+        assert!(out.stdout.contains("Continue? (y/N)"));
+    })
+}
+
+#[test]
+fn test_prompt_fail_if_rustup_sh_already_installed_reply_no() {
+    setup(&|config| {
+        create_rustup_sh_metadata(&config);
+        let out = run_input(config, &["rustup-init"], "no\n");
+        assert!(!out.ok);
+        assert!(out
+            .stderr
+            .contains("warning: it looks like you have existing rustup.sh metadata"));
+        assert!(out
+            .stderr
+            .contains("error: cannot install while rustup.sh is installed"));
+        assert!(out.stdout.contains("Continue? (y/N)"));
+    })
+}
+
+#[test]
+fn test_prompt_succeed_if_rustup_sh_already_installed_reply_yes() {
+    setup(&|config| {
+        create_rustup_sh_metadata(&config);
+        let out = run_input(config, &["rustup-init"], "yes\n\n\n");
+        assert!(out.ok);
+        assert!(out
+            .stderr
+            .contains("warning: it looks like you have existing rustup.sh metadata"));
+        assert!(out
+            .stderr
+            .contains("error: cannot install while rustup.sh is installed"));
+        assert!(out.stdout.contains("Continue? (y/N)"));
+        assert!(!out.stdout.contains(
+            "warning: continuing (because the -y flag is set and the error is ignorable)"
+        ))
+    })
+}
+
+#[test]
+fn test_warn_succeed_if_rustup_sh_already_installed_y_flag() {
+    setup(&|config| {
+        create_rustup_sh_metadata(&config);
+        let out = run_input(config, &["rustup-init", "-y"], "");
+        assert!(out.ok);
+        assert!(out
+            .stderr
+            .contains("warning: it looks like you have existing rustup.sh metadata"));
+        assert!(out
+            .stderr
+            .contains("error: cannot install while rustup.sh is installed"));
+        assert!(out.stderr.contains(
+            "warning: continuing (because the -y flag is set and the error is ignorable)"
+        ));
+        assert!(!out.stdout.contains("Continue? (y/N)"));
+    })
+}
+
+#[test]
+fn test_succeed_if_rustup_sh_already_installed_env_var_set() {
+    setup(&|config| {
+        create_rustup_sh_metadata(&config);
+        let out = run_input_with_env(
+            config,
+            &["rustup-init", "-y"],
+            "",
+            &[("RUSTUP_INIT_SKIP_EXISTENCE_CHECKS", "yes")],
+        );
+        assert!(out.ok);
+        assert!(!out
+            .stderr
+            .contains("warning: it looks like you have existing rustup.sh metadata"));
+        assert!(!out
+            .stderr
+            .contains("error: cannot install while rustup.sh is installed"));
+        assert!(!out.stderr.contains(
+            "warning: continuing (because the -y flag is set and the error is ignorable)"
+        ));
+        assert!(!out.stdout.contains("Continue? (y/N)"));
+    })
+}
diff --git a/tests/cli-misc.rs b/tests/cli-misc.rs
index ba00332f22..eb53771f52 100644
--- a/tests/cli-misc.rs
+++ b/tests/cli-misc.rs
@@ -620,7 +620,7 @@ fn install_stops_if_rustc_exists() {
             .contains("it looks like you have an existing installation of Rust at:"));
         assert!(out
             .stderr
-            .contains("restart the installation and pass `-y'"));
+            .contains("If you are sure that you want both rustup and your already installed Rust"));
     });
 }
 
@@ -652,7 +652,7 @@ fn install_stops_if_cargo_exists() {
             .contains("it looks like you have an existing installation of Rust at:"));
         assert!(out
             .stderr
-            .contains("restart the installation and pass `-y'"));
+            .contains("If you are sure that you want both rustup and your already installed Rust"));
     });
 }
 
diff --git a/tests/cli-self-upd.rs b/tests/cli-self-upd.rs
index 10f4079d8e..4eb96e9c01 100644
--- a/tests/cli-self-upd.rs
+++ b/tests/cli-self-upd.rs
@@ -1166,7 +1166,7 @@ fn install_but_rustup_sh_is_installed() {
         fs::create_dir_all(&rustup_dir).unwrap();
         let version_file = rustup_dir.join("rustup-version");
         raw::write_file(&version_file, "").unwrap();
-        expect_err(
+        expect_stderr_ok(
             config,
             &["rustup-init", "-y"],
             "cannot install while rustup.sh is installed",